SOME RECENT OBSERVATIONS on DIGITALIS PURPUREA L. F
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582.951.64:581.4+581.9 MEDEDELINGEN LANDBOUWHOGESCHOOL WAGENINGEN • NEDERLAND • 72-22 (1972) SOME RECENT OBSERVATIONS ON DIGITALIS PURPUREA L. f. HEPTANDRA DE CHAMISSO E. C. WASSINK Laboratory of Plant Physiological Research, Agricultural University, Wageningen, Netherlands 291st Communication (Received 9-VI-1972) 1. INTRODUCTION A sudden startling biological experience was for me the finding, in 1964,i n our experimental garden, of a plant which later appeared to conform to the one mentioned in the title of this paper (pi. I, photo 1). Since this was the starting point, the composition of this paper differs from the normal habit: I will start with our own observations, and present historical notes further on. Digitalispurpurea, belonging to the Scrophulariaceae (pi. I, photo 2) normal ly has a sympetal corolla of a trumpet or rather prolonged bell shape on which four stamens, 2 longer ones and 2 shorter ones, are implanted (text figure 1). The corolla can be considered as composed of five leaves, thetw odorsa l(adax - ial) ones still more strongly fused than the other ones, while the (5th) stamen, to beexpecte d between these,normall y is lacking. In the deviating plant from 1964, the corolla consisted of a short proximal rim, from which emerge a bilingual, dorsal, bandshaped petaloid structure and, furthermore, seven stamens, standing free, and protruding outside the flower in all directions (see also plate V, photo 10, representing a similar plant, photo graphed in 1968,se e below). Seeds of the 1964 plant were collected and descendents were raised in subse quent years. With some ups and downs, we succeeded in propagating the de viation until now, and in 1968 and later some more detailed examinations were made. The observations, made in 1968 and 1969 will be described here in some de tail, followed by some historical notes, and an outlook on further experimental possibilities and problems. Meded. Landbouwhogeschool Wageningen 72-22 (1972) 1 Textfigure 1 . a. Digitalispurpurea L. Corolla slit open, indicating its composition offive element s (marked 1, 2, 5,6 ,an d 9),th e twoshor t stamens (marked 3 and 4), and thetw olon gstamen s (marked 7 and 8). The numbering as indicated is consistent with what has been used in this paper with regard to the heptandra form (see below). b. Thymus vulgaris L. c. Marrubiumvulgare L. Thefigures b and csho w increasing split between the elements 1 and 2, as is mostly found in Digitalispurpurea, f. heptandra. - a, b,an d cdraw n by Miss M. E. VAN DEN NOORT, after BERG and SCHMIDT (ref. 19). 2. DESCRIPTION OF SOME FORMS AROUND D. PURPUREA F. HEPTANDRA Plants, fairly identical with the original one, occurred in our cultures in sub sequent years, from seeds of the original plant and its descendents in free polli nation. However, they were accompanied by forms somewhere intermediate between the real heptandra and the normal form, or passing 'beyond' heptandra in staminification of the corolla, so that flowers were formed which, in the full possession of the normal calyx and gynoecium, presented nine more or less fully staminiferous elements. The photographs 3-16 (plates II-VIII) represent plants of the various types (black and white reproductions from color slides, taken in our experimental fieldi n 1968an d '69),showin g successive stages of degeneration of the corolla. Plates IX-XII (photo's 17-24) showa series ofisolate d spikes, demonstrating the same phenomenon. Plates XIII and XIV (photo 25) show a series of dried flower types, collected in 1968 from various plants. Theclos esequenc eo f devia tions is obvious. Some discussion on this fact willb epresente d below. Plate XV (figures 1-9) shows analytical drawings of flowers with different degrees of staminification of the corolla. A perusal ofth e mentioned photographs and figures givesris e to the following remarks. Normally, in Digitalispurpurea, the lower labellum of the corolla is somewhat longer than the upper one. An indication of a tendency towards deviation some- Meded. Landbouwhogeschool Wageningen 72-22 (1972) times is the appearance of a somewhat shorter corolla with a more or less straight circular rim (plate XIII). Also otherwise deformed complete corollae show up, with narrower corollar tubes and more pronounced lobes at the rim, seee.g . plate I, photos 3an d 4; that these types could well belong to the same series of deviations is indicated by some of theflowers, highe r up in the spike that showsplittin go fth ecoroll aan dprotrusio n ofsom eanthers , unfortunately, sufficient attention was not paid to this when the photograph was taken. The next stepi sth e appearance of indications of additional anther formation at the rimo fth ecoroll aa tth eexpens eo fcorolla rpart s(plat eXV fig., 1) .A subsequen t stage of corollar degeneration shows a more or less broad dorsal corollar ele ment with lateral anthers, whereas the lower lip is represented by a broad filament withcorolla rappearance ,an da larg eanthe ra tth eto p(PI .XV fig., 2) . Before proceeding with more details, it may be useful to point out that un derstanding of these deviations willi.a . require an examination of development oforgan si nth ebud sfo r whichmateria l hasbee ncollecte dbu tno tye texamined . Until then wewil ltak e what weconside r asth e simplest starting point, andas sume that the entire range of forms can be understood by the assumption that therear e5 corollarelement san d4 staminiterou sones ,thu stogethe r 9,o fwhic h thecorolla rone sar eliabl et odifferen t grades of staminification. It should fur therb eobserve dthat ,i nth enorma lform ,th edorsa lpar to fth ecoroll ai so frathe r uniform colour (red,pin ko rwhite) ,whil eth elatera l andlowe rpart sbea rroun d spots,eac hwit ha dar k centrean d abrighte rare aaroun dit ,a patter nwhic hha s been interpreted as serving to guide insects towards the nectar (the 'honey- mark'). Inth edeviatio nshow nPI .XV fig., 2 ,th ebroa dfilament o fth eabaxia lstame n still bears the insect guiding design. The next step is formed by types in which the lateral stamens have theirfilaments detache d from the dorsal corollar ele ment (PI. XV, fig. 3), also these lateral newly formed stamens may bear the insectguidin gmark so nthei rfilaments. Interestingly ,th estaminiferou s develop mentlef t andrigh ti sno talway sexactl yth esame ,se ee.g .PI .XV fig., 4 ,i nwhic h theadditiona llatera lstame na tth erigh tsid e(n o6 ) stillbear sth epetaloi dmark s onit sfilament, whil eth elef t one(n o5 )ha sa 'normal ' filament. Wewil lintroduc eher ea numberin go fth eelement si na flower o fth e'heptan - dra' typewhic hi st ob econsidere d asmor e orles slogica lfro m our preliminary interpretation of the relation between corollar and staminiferous elements in dicated above.Thus ,w ewil ldenot eth emos tpersisten t dorsal petaloid element as 1, 2(fused) ; thestamen s 3 and 4neares t tothi sar eth enorma l shortstamens , thenewl yforme d lateral stamens,jus t discussed, are 5an d 6,whil e 7an d 8ar e thenorma llon gstamen s; thelowe r(ventra l or abaxial)newl yforme d stameni s elementnumbe r9 . In thetypica l heptandra, theelement s 5,6 ,an d 9 are completely staminified and no more distinguishable from the 'real' stamens 3, 4, 7, and 8. Still, also here,type sdifferin g in degrees,o f dissolution ofth ecoroll a aredistinguishable . So,e.g. ,i nPI .XV fig., 5 ,th edorsa lcorolla relement s 1 and2 stil lar ecompletel y fused, while,i nfig. 6 (th emos ttypica l 'heptandra') the splitbetwee n elements1 Meded Landbouwhogeschool Wageningen 72-22 (1972) 3 and 2 is very pronounced. Different degrees of splitting are distinguishable (see the photographs), ultimately leading to fairly complete staminification of the corolla (see, e.g., PI. XV, figs 8, 9). So far, I have never seen a flower in which complete anthers have developed on the elements 1an d 2; the nearest approach are formations which could be indications of single anthers (PI.XV , fig.9) , or more orles s rudimentary anthericdevelopment swhic hma ydiffe r at bothside so fth eflower (PI .XV fig., 8 x ).A ninterestin gpeculiarit yshow sPI .XV , fig. 7, in which the dorsal elements has two lateral staminiferous formations (1 and 2), as in PI. XV,figs 8 an d 9, however, with afilamentous elemen t( X ) i n between. One might speculate that this mayb ea rudimentar y 10thelement , or potential 5th stamen, but for areliabl e interpretation of thesesmal lcorolla rre miniscences moreobservation sar eneede d(se eals obelo wan dsectio n 3).I have , sofar , not seenflowers wit h 10 stamens(thos eo f PI.XV figs, 7 ,8 ,an d9 ma yb e denoted as types with 9 stamens; 10-staminalflowers hav e occasionally been mentionedi nliteratur e(se esectio n3) . Small additional corollar elements may be seen at the base of stamens (see, e.g., PI. XV,fig. 6 ,i n the literature indicated as 'lacinulae corollinae')t o which considerable importance has occasionally been attatched in literature; in our opinion, however, this will have to await the resultso fmor ethoroug hmorpho - geneticalresearch . Weconclud e our observations withth e presentation, in somedetail , of afe w characteristic flowers. Plates XVI-XVIII (photo 26,a-1 ) present driedflowers. Photo' s 26a-d re presentflowers, al l grown on the same plant; photographs of the same flowers in fresh state are shown on PI. XIX, photos 27-30; analytical drawings of the same flowers are presented on PI.