mentation liquors were a rich source of a material (to which they gave the somewhat inappropriate name "copro- gen") which was very active in promot- ing the growth of . Third, Light and the Asexual Neilands (4) discovered a family of iron-containing compounds, the fer- richromes, which were also very active Reproduction of Pilobolus in promoting the growth of Pilobolus. Now, hemin, coprogen, and the fer- Responses to light play an role in the richromes have one property in com- important mon: they all contain iron in chelated development and reproduction of this . form. It appears, therefore, that one distinctive nutritional requirement of Pilobolus is that it be supplied with Robert M. Page iron in specially chelated form. Al- though the identity of the material in dung remains unknown, it seems proba- ble, from the work of Lyr (5), that Pilobolus, a fungus assigned to the mals. For example, I have isolated bacteria in the dung are a major source order , differs from all other strains- from such exotic sources as of this growth factor. It is possible, members of this order of terrestrial caribou dung collected near Point therefore, that this factor is similar to Phycomycetes in that it discharges its Barrow, Alaska, and wallaby dung col- coprogen, or that the two are identical. sporangia explosively. Because of this lected at Wilson's Promontory at the In addition to their requirement for spectacular method of dispersal southernmost tip of Australia (1). specially chelated iron, some species Pilobolus has attracted the attention of One question which arises immedi- of Pilobolus have a near-requirement biologists for almost three centuries, ately is, Why does Pilobolus grow on for fatty acids. Growth is very poor in but the is of current interest not dung? To be sure, one species, P. media containing carbohydrates as a only because of the dramatic way in oedipus, has been reported to grow on source of carbon, but growth is vigorous which it is adapted to its environment decomposing algae along river and canal in media containing appropriate concen- but also because it has attributes which banks, but all of the other species have trations of sodium acetate. All of the make it of interest in the study of been found only on dung. Is the genus species of Pilobolus tested have grown fundamental biological problems. restricted to this habitat only by the on synthetic media containing hemin, All of the species of Pilobolus except mechanics of its spore dispersal, or are acetate, a nitrogen source, and in- one occur on the dung of herbivorous nutritional factors involved as well? A organic salts (2). By far the most animals. The mycelium grows beneath partial answer to this question may be active nitrogen source is ammonia the surface of the substratum, and found in the results of nutritional (ammonium ion). Both vegetative after a few days it produces a crop of studies. growth and reproduction are greatly sporangiophores. When each sporan- stimulated by ammonia in certain con- gium reaches maturity it is shot off centrations (6). forcibly, and if, at the end of its tra- Nutritional Requirements It appears from the results of nutri- jectory, it strikes a blade of grass, the tional studies that Pilobolus is bound adheres to it. If a grazing Early attempts to grow Pilobolus on to its habitat as much by its nutritional animal eats a blade of grass with ad- synthetic media of known chemical requirements as by its method of spore herent sporangia, the thousands of composition were unsuccessful. The dispersal, and that its nutrition is as contained within each sporan- fungus grew well only on dung or on specialized as its morphology. More- gium pass unharmed through its di- aqueous extracts of dung. Within the over, from a practical point of view gestive tract and emerge with the dung, past decade, however, investigations in the results of nutritional studies have in which they germinate to repeat this several laboratories have provided some been useful because they have made it asexual reproductive cycle. Pilobolus information on the nutritional require- possible to grow the fungus under much also reproduces sexually in a manner ments of some members of the genus. more rigidly controlled conditions than similar to that of other Mucorales. First, through fractionation of aqueous is possible on a dung medium. Also, the Pilobolus is widely distributed, and extracts of cow dung, it was found that growth and development of the fungus although it is not often observed in the material in dung which was re- can be observed more conveniently on the field because its sporangiophores quired by Pilobolus was heat-stable synthetic media than on natural sub- are ephemeral, it appears frequently and soluble in water but not in fat strata. on samples of dung brought to the solvents. It was not adsorbed by anionic laboratory and kept under moist con- or cationic exchange resins, but it was ditions for a few days (Fig. 1). The strongly absorbed by charcoal and cer- Growth and Development genus has been reported from many tain other nonspecific adsorbants. The parts of the world, and it occurs on the growth-promoting activity of this factor On transparent synthetic agar media dung of many kinds of herbivorous ani- can be imitated by hemin, but relatively it is possible to follow the growth of high concentrations (10 mg/ml) are the mycelium and the development of The author is associate professor in the de- required (2). Second, workers at the the asexual structures of partment of biological sciences, Stanford Uni- reproductive versity, Stanford, Calif. Lederle Laboratories (3) found that fer- Pilobolus in detail (Fig. 2). The my- 1238 SCIENCE, VOL. 138 sporangium, which is later separated from the rest of the sporangiophore by a crosswall. Sooner or later the upper part of the sporangiophore swells to form a conspicuous subsporangial swelling or vesicle, and the wall of the sporangium becomes jet black. In the meantime the contents of the sporan- gium cleave to form a large number of multinucleate spores. As the sporan- gium reaches maturity its wall separates at the base, so that the gelatinous ma- terial surrounding the spores is ex- posed. Finally, the wall of the sub- Fig. 1. Sporangiophores of Pilobolus sp. on cow dung. (About X 5) sporangial vesicle ruptures suddenly just below the sporangium. The sporan- gium is shot off, propelled by the liquid celium, which grows beneath the sur- conditions, the mycelium begins to in the sporangiophore and the empty face of the medium, may be some- form trophocysts, which are first recog- sporangiophore is thrown flat on the what restricted, as in Pilobolus crystal- nizable as swollen regions along certain medium by the recoil. linus Fries and its relatives, or it may hyphae. These swellings enlarge as The force with which the sporangia spread rapidly to fill the medium in a protoplasm flows into them, and finally are discharged is impressive. Sporangia petri dish in a few days, as is the case each trophocyst is completed by the which strike the lid of a petri dish with P. kleinii van Tiegh or P. sphaero- formation of crosswalls which isolate it make a clearly audible "plink," and sporus Palla. The mycelium is coeno- from the parent hypha. Later, a stout those whose progress is not interrupted cytic; the hyphae are devoid of cross- hypha, the sporangiophore, grows from are thrown for remarkable distances. walls except for those which delimit each trophocyst, increases in length, All records for altitude and distance are reproductive structures or wall off small emerges from the medium, and con- held by sporangia reported by Buller branch hyphae from which the pro- tinues to elongate in the air. After a (7); he found that large sporangia toplasm has been withdrawn. Sooner or time the sporangiophore stops elongat- of Pilobolus kleinii and P. longipes are later, depending on the species and ing and its tip swells to form the shot to a height of 6 feet 0.5 inch.

.... : - . 0 :. :-, C)

0

Fig. 2. Schematic drawing (based on P. crystallinus) showing the development of asexual reproductive structures of Pilobolus. Trophocysts and sporangia are represented as developing in clockwise sequence on hyphae emanating from a sporangium.

14 DECEMBER 1962 1239 When sporangiophores were aimed at form sporangia in the dark, P. sphaero- a 45-degree angle above the horizontal, sporus is more suitable for studies on the maximum range was 8 feet 0.5 inch periodicity, and it has been shown to for P. kleinii and 8 feet 7.5 inches for have an endogenous rhythm which is P. longipes. susceptible of entrainment (11). From the maximum height to which The phototropic responses of Pilobo- sporangia are shot, Buller calculated lus have been studied far more inten- that the muzzle velocity would be 19.6 sively than its morphogenic responses feet per second if air resistance is to light (12). It is well known that neglected. Pringsheim and Czurda (8) the fungus discharges its sporangia attempted to measure the muzzle veloc- toward a source of light, and the ity directly by allowing sporangia to accuracy with which the sporangio- pass through holes in a rotating disk phores direct the sporangia at an illu- and strike a second disk rotating on the minated target has been demonstrated same shaft. From the results, they cal- by many workers. To illustrate this culated that the muzzle velocity was Fig. 3. Sporangia of Pilobolus kleinii ad- accuracy, a target of translucent paper approximately 14 meters per second. hering to a paper target of which the was attached to the underside of the In order to avoid some of the errors center was illuminated (see text). lid of a container that was opaque ex- inherent in this technique, Donald Ken- cept for a hole 1 centimeter in dia- nedy and I arranged sporangiophores meter behind the bull's-eye of the of P. kleinii in such a way that, in exposed to visible light of various wave- target, and a culture of Pilobolus kleinii their flight, they partially occluded, in lengths from a monochromator, only growing on synthetic medium in a petri succession, two beams of light 3 milli- light of wavelengths shorter than about dish 10 centimeters in diameter was meters apart. The partial interruption 510 millimicrons was effective in in- placed in the container, together with of the beams was detected by a photo- ducing the formation of trophocysts (9). moist blotting paper to maintain the cell connected to an oscilloscope in These spectral limits, together with the relative humidity at a high level. As such a way that the interval between fact that trophocyst formation is sup- shown in Fig. 3, many sporangia struck the interruptions could be measured. pressed by L-lyxoflavin, which is a the bull's-eye of the target, and most Preliminary results indicated that the competitive inhibitor of riboflavin, but of them landed within 1 centimeter of muzzle velocity of relatively small not by diphenylamine, which interferes that circle. In this instance, the target sporangia of P. kleinii ranged from 5 with the synthesis of some carotinoids, was placed 10.7 centimeters above the to 10 meters per second, but further suggest that the photosensitive pigment culture, so that a circle 1.0 centimeter trials will be required to establish the may be a flavin. Of course, other inter- in diameter subtended an arc of ap- range of velocities for this and other pretations are possible, but in any case proximately 5 degrees. Thus, most of species more precisely. it is interesting that this step, which the sporangia struck the paper within requires light in P. kleinii, can be car- about 5 degrees of the illuminated ried out in complete darkness in other center of the target, despite the fact Response to Light species. that sporangia near the margin of the is capable of petri dish were aimed at a considerable All of the stages in asexual reproduc- forming trophocysts and sporangio- angle to the vertical. Of course, the tion which precede the dramatic and phores in continual darkness, but the fungus has no means of compensating climactic discharge of the sporangium sporangiophores become abnormally for the effect of gravity on the tra- are influenced by light. Indeed, it would long-up to several centimeters, as com- jectory of the sporangium, so its be difficult to overemphasize the im- pared with the usual length of about accuracy decreases as the distance to portance of light in the life of Pilobolus, 0.5 centimeter-and sporangia do not the target is increased. because almost all of its activities are form unless the culture is exposed to In order to observe the morphological affected by this environmental factor. light. Brefeld reported similar behavior aspects of the phototropic responses For purposes of discussion, the re- in P. microsporus (10). Pilobolus which precede the discharge of spo- sponses of the fungus to light may be sphaerosporus, on the other hand, not rangia toward light one must study divided into two categories: morpho- only produces normal sporangiophores sporangiophores at two stages in their genic responses, in which the response but forms and discharges sporangia in develoment, because positive phototrop- is not oriented, and tropisms, in which continual darkness. However, even ism is shown both by young sporangio- the direction of the response is related those species which are able to form phores which have not begun to form to the source of the stimulus. part or all of the asexual reproductive a sporangium and by mature sporangio- Various species of Pilobolus differ in apparatus in darkness produce more phores in which the subsporangial vesi- their morphogenic responses to light. structures after exposure to light. cle has attained its full size. The tech- Pilobolus kleinii, for example, requires All species of Pilobolus form spo- nique used to study the phototropism of light for the first step in the develop- rangia periodically when exposed to a sporangiophores at both stages was, ment of the asexual reproductive ap- suitable daily alternation of light and briefly, as follows. The fungus was paratus, the development of trophocysts. darkness. Pilobolus kleinii, for example, grown on synthetic media in petri The mycelium of this species grows begins to discharge sporangia about 3 dishes, and after the mycelium was vigorously in the dark, but no tropho- hours after the beginning of the light established, the cultures were subjected cysts are formed unless the specimen is period when grown on a schedule of to 8 hours of light followed by 16 hours exposed to light. Only a brief exposure 12 hours of light and 12 hours of dark- of darkness daily to induce the forma- is required, and when mycelia were ness per day. Because of its ability to tion of sporangiophores. Blocks of agar 1240 SCIENCE. VOL. 138 Fig. 4. Response of a young sporangiophore of Pilobolus kleinii to unilateral illumination. Photomicrographs were taken at 10- minute intervals. with sporangiophores at an appropriate time it appears to be sharply but crystallinus are bent to an angle which stage of development were cut from smoothly bent toward the light. Oc- is consistently less than the angle be- these cultures. Each block was laid on casionally, as in the sporangiophore tween the light and the former axis of its side on a cover glass, which was illustrated, the new growth is initiated the sporangiophore. then inverted to form the top of a small farther from the tip, so that the Mature sporangiophores resemble chamber mounted on a microscope original tip remains visible. In such a young ones in that they exhibit positive slide, so that the sporangiophores could case, the response may be said to phototropism, but they respond by be viewed from the side with a micro- consist of the formation of a branch on bending toward the light rather than scope fitted with a 3X objective. Light the illuminated side of the sporangio- by initiating growth in a new direction from a small microscope lamp was phore. (Fig. 6). Here again the response is passed through heat-absorbing glass and The response of young sporangio- preceded by a lag phase, but this directed on the sporangiophores through phores of Pilobolus crystallinus to uni- appears to be much shorter in the a window in the side of the chamber. lateral illumination appears to be mature sporangiophores. It is difficult Red light from a photographic safelight basically similar to that of P. kleinii, to determine the minimum length of this mounted in a second microscope lamp but there is a puzzling difference. As period precisely, because of difficulties was focused on the sporangiophores by shown in Fig. 5, the sporangiophore of in recognizing fully matured and re- the condensing lens of the microscope P. crystallinus also stopped growing sponsive sporangiophores and in detect- to provide illumination for observation when the light was directed on it ing the first traces of bending, but and photomicrography. Photomicro- from one side, and after a time growth curvature of sporangiophores of graphs were taken at intervals of 5 or recommenced, after the initiation of a Pilobolus kleinii has been observed 10 10 minutes. new tip on the flank of the old one. In minutes after the beginning of unilateral These observations showed that all cases observed the new tip was illumination. This figure is in agreement young and mature sporangiophores formed close to the original one, so with that of Buller (7), who reported differ considerably in the way in which branching was not evident. The sporan- the period of latency in P. longipes to they respond to unilateral illumination, giophores of P. crystallinus differ from be 10 minutes. and that the response of young spo- those of P. kleinii in that they do not After a lag period the sporangiophore rangiophores of Pilobolus kleinii differs grow more or less directly toward the begins to bend in a region just below in some respects from that of young light but grow toward a point above the subsporangial vesicle. The rate of sporangiophores of P. crystallinus. The the light. Thus, after growing for some bending increases and within a few nature of the phototropic response of a time, young sporangiophores of P. minutes reaches a maximum, which young sporangiophore of P. kleinii is revealed by the series of photomicro- graphs shown in Fig. 4. When the spo- rangiophore was exposed to unilateral illumination it stopped growing. After about an hour a protuberance appeared on the illuminated flank of the dome- shaped tip of the sporangiophore, and this protuberance soon assumed the shape and character of a sporangio- phore apex. Growth from this new tip continued in the general direction of the light until the sporangium began to form. Usually the new tip is formed close to the original one, so that after a Fig. 5. Response of a young sporangiophore of Pilobolus crystallinus to unilateral sporangiophore has elongated for some illumination. Photomicrographs were .taken at 20-minute intervals. 14 DECEMBER 1962 1241 Fig. 6. Phototropicresponse of a mature sporangiophoreof Pilobolus kleinii. The first photomicrographwas taken approximately 1 hour after the beginning of unilateral illumination and the others, at 5-minute intervals thereafter. varies from 1.1 to more than 4 degrees adjacent to the sporangium acts as an rangium is not directed toward a source per minute. Bending continues at almost optical filter which reduces the inten- of light, the rays which enter the the maximum rate until the sporangio- sity of light striking the pigmented vesicle are concentrated on the wall, phore bends beyond the beam of inci- zone at the base of the vesicle as the but when the sporangium is aimed di- dent light; then the bending slows sporangiophoreapproaches the beam of rectly at the light, the rays are directed rapidly and reverses direction. A fully light. to the base of the vesicle in the vicinity mature sporangiophore of Pilobolus Buller (7) suggested that the up- of a ring of protoplasm which contains kleinii reaches its maximum curvature per pigmented zone might function an orange-red pigment. Thus, according about 1 hour after the beginning of in triggering the discharge of the spo- to Buller, a sporangiophore is an unilateral illumination. rangium by increasingthe osmotic pres- ocellus which is in physiological equilib- sure of the cell sap or weakening the rium when the sporangium is aimed wall of the subsporangial vesicle at directly at a source of light. Buller's Proposed Mechanisms the point where rupture occurs, but hypothesis also explains the fact that the position of this zone makes it ap- mature sporangiophores exposed to That the sporangiophore overshoots pear equally likely that it could func- two sources of light simultaneously aim is shown in Fig. 6, and if the curvature tion as a screen which would tend to toward one light or the other when of a unilaterally illuminated maturing damp oscillation and act as a "fine ad- the angle between them exceeds a cer- sporangiophore is plotted against time, justment" in aiming the sporangio- tain value (about 10 degrees). In fact, the resulting curve (Fig. 7) shows that phore. his explanation of the optics of photo- the sporangiophore may bend past the The optical aspects of the phototropic tropism was stated with such logic beam of light several times. Although response of mature sporangiophores and clarity that it may have discouraged the measurements were made too in- were studied intensively by Buller, who further investigation, because it created frequently to give a detailed picture, was a pioneer in the application of the the impression that all problems had the curve gives the impression of be- principles of optics and mechanics to been solved. ing the record of a damped oscillation. the solution of biological problems. By Although the optical properties of It may be that the lag which precedes means of diagrams constructed care- young sporangiophores appear simpler the onset of bending is partially re- fully on the basis of the refractive in- than those of the mature structures,they sponsible for the damping action. It dices of the wall, cytoplasm, and cell must be reexamined in view of the is also possible that the pigment which sap of the sporangiophore, Buller (7) discovery that young sporangiophores is present in the cytoplasm at the demonstrated that the subsporangial respond by initiation of growth on the shoulder of the subsporangial vesicle vesicle acts as a lens. When the spo- illuminated side of the tip. Most in-

1242 SCIENCE, VOL. 138 vestigatorshave assumed that the young from sporangiophores. He found a Limits of Spectral Sensitivity sporangiophoreof Pilobolus responds in close resemblance between the action the same way as Phycomyces, another spectrum and the absorption spectrum, It seemed desirable, therefore, to member of the order Mucorales. Buder and found that the absorptionspectrum, determine the limits of spectral sensi- (13) proposed that in Phycomyces the in turn, resembled the absorption spec- tivity by a differentmethod. Both young sporangiophoreacts as a cylindricallens trum of beta carotene. For over a and mature sporangiophores were ex- which concentrates light on the cyto- decade the conclusion, drawn from posed to light of various wavelengths plasm inside the wall farthest from the these results, that the active pigment through projection of a spectrum on light, and that curvature results from was a carotinoid was accepted, but cultures. After being passed through an increase in growth in this region. after it was suggested (16) that flavins heat-absorbingglass and suitable neutral The results of most experiments have might be involved in phototropism of density filters, light from an incandescent supported this hypothesis for Phy- higher plants this interpretation was lamp was passed through a slit and comyces, but for Pilobolus it is difficult questioned, because it is difficult to focused on a collimating lens before to reconcile the hypothesis with the distinguish between the two classes of being dispersed by a prism and directed observation that the response of the pigments on the basis of action spectra. on the culture by a second lens. The young Pilobolus sporangiophoreoccurs An additional complication was intro- apparatus was calibrated by placing a on the side nearest- the light. In duced by Jacob (17), who determined fluorescent lamp in front of the slit Pilobolus reflection from the surface the limits of spectral sensitivityof young and noting the positions of the emis- appears to be far more important than sporangiophores of Pilobolus both by sion lines of mercury. Slabs of synthetic refraction by the contents of the means of interference filters and by agar medium with sporangiophores at sporangiophore. means of cadmium- and zinc-filled gas the proper stage of development were If the cylindrical lens hypothesis is discharge tubes with glass filters. He cut from petri-dish cultures which had no longer tenable for Pilobolus, a con- found that young sporangiophores of been grown under conditions of alter- venient explanation for the fact that certain strains of some species were nating light and darkness to induce young sporangiophoresof P. crystallinus sensitive to wavelengths as long as 660 synchronous development of sporangia, do not grow directly toward a source m/u. and the slabs were placed in a clear of light is eliminated. Sporangiophores of Phycomyces also bend to an angle that is less than that between a source of visible light and the former axis of the sporangiophore. Varju, Edgar, and 90 Delbriick (14) have explained this phenomenon as being due in part to the fact that light is refracted in a complex pattern by a tilted cylindrical lens and in part to the combined effects of light and gravity. The effect of gravity may be dis- co counted in the case of Pilobolus crys- w n tallinus, because its sporangiophores Cc 60 are only weakly geotropic (a recog- 0 nizable geotropic curvature is de- tectable only after the sporangio- w phores have been allowed to elon. gate in the dark for several days); moreover, under the conditions of our study, the sporangiophores were hori- -). zontal, so that a geotropic response would have been at right angles to the : 30 plane of observation. Thus, the be- .30 havior of young sporangiophores of Pilobolus crystallinus remains a puz- zling phenomenon, for which no ex- planation is at hand. Another question not yet answered with certainty is, What is the nature of the visual pigment in Pilobolus? One of the first attempts to identify this photo- sensitive pigment was that of Biinning (15), who measured the phototropic response to light of various wave- lengths obtained by means of glass and I 2 3 4 5 liquid filters and compared the action TIME (HOURS) spectrum so obtained with the absorp- Fig. 7. Graph showing the response of maturing sporangiophore of Pilobolus kleinii tion spectrum of pigments extracted to unilateral illumination. 14 DECEMBER 1962 1243 exposed to light; the relatively crude phototropic response of young spo- rangiophores permits them to grow out of crevices and away from the sub- stratum; the precise phototropism of mature sporangiophores guarantees that sporangia will be shot toward the sun or open sky; and the timing of sporan- gial discharge-in some species, at least-is such that the range is nearly maximal. But teleology is unfashion- Fig. 8. Sporangia of Pilobolus sphaerosporus adhering to a glass plate interposed able; moreover, the series of events between a culture and a light dispersed by a prism. The distribution of the sporangia which culminates in the explosive dis- a crude action for gives spectrum phototropism of mature sporangiophores. charge of the sporangium is only the first stage in a system of asexual repro- duction. The second stage, in which the plastic box with a saturated sponge to were clear-cut. Most of the sporangio- spores are transported passively inside maintain the relative humidity. phores exposed to wavelengths shorter the digestive tract of an animal, is less The response of mature sporangio- than about 546 m,x were bent in the dramatic but results in transport over phores was recorded by placing a plate direction of the light, and the response far greater distances. It should be of glass in the box between the fungus appeared to be particularly strong be- emphasized that all aspects of asexual and the light. If a sporangiophore re- tween about 410 and 520 myt. The reproduction-the subtle as well as the sponded to light of a given wave- pattern of response of one strain of P. striking-are important, because they length it shot its sporangium toward kleinii was similar, but the demarcation are part of a system. Since this system the plate; if it did not respond, it dis- between response and no response was depends on all of its components, charged its sporangium in a random less clear. In two out of three trials no Pilobolus could not have evolved prior direction. Thus, the pattern of sporan- response was observed at wavelengths to the advent of herbaceous angio- gia adhering to the glass gave not only above 546 mjt, but in one trial the up- sperms and grazing mammals. The pres- an indication of the limits of spectral per limit was between 546 and 578 mtn. ent widespread distribution and fre- sensitivity but also a very crude action Although the technique used for quent occurrence of the fungus are spectrum. these trials was far too crude to permit objective and eloquent testimonials to The response of mature sporangio- us to draw conclusions with regard the survival value of its system of phores was determined by direct ob- to the nature of the photoreceptor, the asexual reproduction. servation. A plate of glass with the results are compatible with the sug- Most of the information accumulated paths of the emission lines of mercury gestion that it is either a carotinoid or a on asexual reproduction in Pilobolus marked on it was laid in the bottom of flavin. Since there was no clear re- has been descriptive of the more spec- the plastic dish, and slabs of agar sponse of young sporangiophores to tacular and obvious features. It is to medium with young sporangiophores wavelength greater than about 580 mt, be hoped that in the future more at- that had just emerged from the medium the results failed to confirm those of tention will be devoted to some of the were laid on the plate. After the spo- Jacob. It seems probable that this subtler aspects. The status of our rangiophores had been exposed for difference should be ascribed to differ- knowledge of phototropism in Pilobolus several hours to the light dispersed by ences in the species and strains of the is very elementary as compared with the prism, those on portions of the plate fungus, but it is also possible that the detailed analyses of the behavior of illuminated by light of wavelengths to differences in light intensity are in- Phycomyces sporangiophores made by which the sporangiophores respond volved. The fact that Entomophthora Castle, Delbriick, Shropshire, and others appeared to lie in windrows, because coronata (= Conidiobolus villosus), (19). The biochemical mechanisms in- they were all growing toward the light, another terrestrial phycomycete, re- volved in phototropism have not been whereas those on other portions of the sponds to wavelengths as great as 630 studied. Even the nature of the photo- plate stood erect or were bent at my indicates that red light can be ab- receptive pigment is not known-nor is random. sorbed by some fungus photoreceptors it known in Phycomyces and higher The results indicated that mature (18). plants. Perhaps more significant is our sporangiophores of a strain of Pilobolus ignorance of the chain of events that kleinii respond to wavelengths between lie between the reception of light by 400 and 550 m,u, but the lower limit Conclusion this as yet unknown pigment and the of sensitivity could not be established formation of wall material. with certainty, because of scattering The responses of Pilobolus to light, Indeed, information on this aspect of light by the optical system. Mature as well as its specialized nutrition, are of phototropism might contribute to an sporangiophores of P. crystallinus re- manifestations of the adaptation of the understanding of some general aspects sponded to a similar range of wave- fungus to its environment, and some of morphogenesis in fungi. In coeno- lengths, but those of P. sphaerosporus of the aspects of asexual reproduction cytic organisms, such as Pilobolus, the responded strongly to wavelengths be- are so striking as to make teleological body is basically a tube which swells tween 430 and 540 m/A, with a maxi- interpretation a temptation. For ex- in certain localized areas as a result mum response at about 480 myt (Fig. 8). ample, the periodic formation of spo- of synthesis of wall material; in fact, The results obtained with young spo- rangia ensures that sporangiophores all structures formed by Pilobolus could rangiophores of Pilobolus crystallinus will be at a reactive stage when they are be accounted for by two mechanisms:

1244 SCIENCE, VOL. 138 one which would bring about localized References and Notes 11. D. L. McVickar, Am. J. Botany 29, 372 (1942); D. T. Klein, Botan. Gaz. 110, 139 synthesis of wall material to produce 1. I am grateful to Mrs. Galen Hilgard and (1948); A. Schmidle. Arch. Mikrobiol. 16, swellings, and one which would form Dr. I. L. Wiggins for these collections. 80 (1951); E. R. Ubelmesser, ibid. 20, 1 2. R. M. Page, Am. J. Botany 39, 731 (1952). (1954). crosswalls to delimit the structures. 3. C. W. A. R. C. Hesseltine, Whitehill, Pidacks, 12. G. H. Banbury, in Handbuch der Pflanzen- Since in Pilobolus it is M. TenHagen, N. Bohonos, B. L. Hutchings, physiologie, W. Ruhland, Ed. possible through J. H. (Springer, Williams, Mycologia 45, 7 (1953). Berlin, 1959), vol. 17, pt. 1, p. 530. suitable manipulation of light to deter- 4. J. B. Neilands, Bacteriol. Revs. 21, 101 13. J. Buder, Ber. Deut. Botan. Ges. 36, 104 mine the regions in which wall synthesis (1957). (1918). 5. H. Lyr, Arch. Mikrobiol. 19, 402 (1953). occurs, it may be possible to study the 14. D. Vl,rju, L. Edgar, M. Delbriick, J. Gen. 6. R. M. Page, Am. J. Botany 46, 579 (1959); Physiol.-' 45,s 47 (1961). Mycologia 480 biochemistry and fine structure of 52, (1960). 15. E. Bunning, Planta 26, 719 ibid. 7. A. H. R. Buller, Researches on Fungi (1937); 27, 148 (1937); ibid. 27, 582 (1938). these regions and thus explore a signifi- (Longmans Green, New York, 1934; Hafner, 16. A. W. Galston and New York, 1958), vol. 6. R. S. Baker, Am. J. cant and intriguing channel in the 773 8. E. G. Pringsheim and V. Czurda, Jahrb. Botany 36, (1949). archipelago of events which stretches Wiss. Botanik 66, 863 (1927). 17. F. Jacob, Arch. Protistenk. 103, 531 (1959). between genetic information and 9. R. M. Page, Mycologia 48, 206 (1956). 18. R. M. Page and J. Brungard, Science 134, phys- 10. 0. Brefeld, Sitzber. Ges. Naturforsch. 733 (1961). ical shape. Freunde zu Berlin 1877, 1 (17 Apr. 1877). 19. W. Shropshire, in press.

NEWS AND COMMENT ployees by evolving into a useful serv- ice organization for training techni- cians and developing international standards in such areas as health, safety, and waste disposal. It has also sponsored what are generally regarded Nuclear Energy for India: U.S. Position as extremely useful conferences and on SafeguardsRaises Concern of IAEA symposiums on a wide variety of sub- jects related to the peaceful develop- ment of atomic energy. However, the agency's failure to make any headway in a safeguards or Supporters of the International came along far more slowly than was inspection role has been a constant Atomic Energy Agency (IAEA) are expected when Eisenhower first made source of concern to its supporters, readying mourning bands and casting his proposal. Thus there proved to be since this role has been regarded from accusatory looks toward the Kennedy no immediate grounds for fears that the first as the main justificationfor the administration, despite public and pri- nations newly equipped with power agency's existence. The creeping devel- vate assurances that the administration reactors could surreptitiously divert opment of nuclear energy has until is dedicated to promoting a bright fu- nuclear materials to weapon produc- recently provided an explanation for ture for the IAEA. tion. In the meantime, the two major this failure, but the safeguards issue There is substantial evidence that a nuclear powers had entered into a has now presented itself in a concrete bright future is, in fact, what the ad- large number of bilateral agreements form, namely, India's decision to buy ministration wishes for the IAEA; but with nations seeking the benefits of a 380-megawatt nuclear power plant the matter is not a simple one, and nuclear technology. The bilateral agree- from this country. friends of the agency can be forgiven ments, of which the United States now if they conclude that there is a disturb- has 44 and the Soviet Union 14, were India's Plans ing discrepancy between American in most instances preferred by the re- There is no doubt that there will be words and deeds. cipient nations, who came to look outside inspection of the Indian plant; This discrepancy has been evident upon a nation-to-nation relationship as the United States has made it clear throughout the 5-year history of the more prestigeful than assistance chan- that it will not permit shipment of the IAEA, an organization that slowly and neled through the IAEA. This feeling nuclear materials unless it has ironclad painfully grew out of the Atoms-for- was fostered by the Soviets' traditional assurance that the installation opera- Peace proposal put forth by President aversion to international inspection, tions will be open to trustworthy Eisenhower in 1953. Now numbering and, politically, it put the United States inspection. Rather, the question is 78 member nations, IAEAis a large and in a poor competitive position when whether the inspectors will come from busy enterprise, devoted in large part lesser-developed nations suggested they this country or from the IAEA. The to communicating peaceful nuclear would look toward the Soviets if the agency regards the decision as an ex- technology to underdeveloped nations. United States insisted upon working tremely critical one for its future since But the original justification for its through the IAEA. In all bilateral ar- the Indian installation, larger than any founding-to provide assurance that rangements, the United States and, pre- that has yet been sold abroad, would the major nuclear powers, in spreading sumably, the Soviets have insisted that for the first time give a nuclear have- nuclear technology, would not be con- their own inspection and safeguards not nation the capacity for acquiring tributing to the spread of nuclear weap- accompany assistance, with the result a sizable amount of weapon-grade ons-has never been realized in actual that the IAEAhas not come to play a plutonium. What disturbs the IAEA is operations. significant role in inspection. that United States officials, apparently The reasons for this failure are tech- The agency, meanwhile, has justified in deference to India's opposition to nical and political. Nuclear power its $7 million budget and 600 em- IAEAinspection, have stated that this 14 DECEMBER 1962 1245