tissues. Yields per acre are tremen- ing and food? Rayon, along with other dous; the young stems are easy to chemical converts, may also be an end harvest and chip with fairly simple and product of the new forest, helping to light equipment. The young wood is clothe our people in generations to relatively uniform in its characteris- come. Sugar, molasses, and yeasts can tics. Bark and leaves are not considered also be derived from wood. They trash in some products. could help considerably to provide the Maybe our young forest of sprouts world with vital and urgently needed will mass-produce raw material for energy foods and proteins at low cost. mass-produced housing to help shelter Thus, the silage connotation in the our exploding population. What about designation "silage sycamore" may the other two necessities of life—cloth- not be so weird after all.

The Brain and the Egg

RAYMOND D. SCHAR

Mother Nature originally groups of chickens that gradually be- intended the egg of a bird to be used came more and more proficient in exclusively to perpetuate the species. their ability to produce eggs. As the To accomplish this parental instinct, birds were kept confined to smaller the bird was endowed with internal areas, they could no longer forage for organs and glands that responded to their feed. Man became the provider. certain external stimulations that oc- Through trial and error, he learned curred in nature. However, man has that a chicken would lay more eggs altered many of these external stimu- when fed one kind of feed than lants in order to force the domesticated another. By observing that a hen fowl to better serve him. began to produce more eggs in the The domesticated chicken is thought spring of the year as the days became to have originated from the jungle longer, man reasoned correctly that if fowl. This ancestor laid her eggs in he provided artificial light to lengthen the spring and early summer months the day, she would lay more eggs. Pro- as the length of the days increased. tection against the elements and dis- She woxild lay 10 to 12 eggs, incubate eases permitted additional production. them, and brood the chicks, and then All these efforts down through the repeat this process once and occasion- centuries have increased yearly egg ally twice. When man discovered the production from 20 to 30 eggs per hen egg was a good food, he started to to 250 and above in the better pro- domesticate chickens. By taking the ducing strains. But modern man is not eggs from the hen's nest as she laid content. He is intensifying his efforts them, man disrupted her normal to produce an even more prolific reproduction cycle. Since she no chicken. Refined selection principles, longer had to incubate her eggs and crossing and incrossing of families and brood the chicks, her body underwent physiological adjustments that per- RAYMOND D. SCHAR is Coordinator, National mitted her to lay more eggs. Poultry Improvement Plans, Animal Husbandry Through selection, man developed Research Division, Agricultural Research Service. 44 Chicken egg seems minute compared with egg from biggest bird ever known, Madagascar's elephant bird, extinct for centuries. National Geographic Society, which found giant fossil egg, estimates that when fresh it weighed about 20 pounds, equal to 160 hen eggs.

strains, fortified diets, and improved time of artificially stimulated ovula- environmental conditions are but a tions to be reliably measured. few of the practices under constant Some of the earliest studies of ovula- study and improvement. In addition, tion led to the conclusion that light is during the last several decades, this probably the main external stimulus never ending search for perfection has to egg production. Since the hen's eye drawn a new group of scientists into picks up the light and sends signals to the picture. These are the physiologists. the brain, it was reasoned that the The physiologists are studying the brain must be the initial biological functions and activities of the organs clock involved in ovulation. It was and glands to find their relationship also discovered that the anterior pitui- to each other and to determine the tary gland, located directly beneath effects of natural and artificially in- the brain, is the organ responsible for duced internal and external stimuli. secretion of the hormones which are Dr. Richard M. Fraps, while a necessary for ovulation. physiologist at the University of Chi- The portion of the brain known as cago, investigated the effect of hor- the hypothalamus apparently is di- mones on feather development in rectly responsible for the initial inter- chickens. In time, he expanded his nal stimulation. This was verified when interest in hormones to include the ovulation was consistently induced by part they played in ovulation. Since the infusion of extracts from the hy- the ovaries of birds produce eggs that pothalamus into the pituitary gland. rnature singly, chickens provided an Conversely, intentional injury to the excellent opportunity for this study. hypothalamus stopped ovulation for A domestic hen will complete an extended period. Also, when cer- more than 200 ovulations a year in tain drugs known to affect the nervous rather definitely established cycles. system were injected into the hen, the This allows a reasonably accurate ovulation cycle was disrupted. How- estimate to be made of the time of ever, if extracts from the hypothalamus natural ovulation, thus permitting the were injected into birds from which the 45 STIMULI saclike membrane which surrounds the single, fully developed yolk. This per- mits the yolk to be released from the ovary. The infundibulum, or upper end of the oviduct, then engulfs this free yolk and starts it on its journey down the hen's reproductive tract. Besides causing maturation and ovu- lation of a yolk, the pituitary-secreted hormones cause the ovary to secrete hormones of its own. These are thought to be estrogens and progestagens and are called feedback hormones. When they reach the hypothalamus, they cause a signal to go to the pituitary which inlubits its hormone produc- tion, completing the cycle. After Dr. Fraps came to work for the U.S. Department of Agriculture at Beltsville, Md., he and his coworkers studied time patterns involved in the intricacies of ovulation. After repeated experiments and observations, they de- termined that release of LH closely re- lates to the onset of darkness in the light/dark cycle of the day (or other light/dark cycle from 22 to 34 hours in length). In most instances, the mem- brane or follicle surrounding the yolk Hormone secretion and flow in hen^s ruptures about 8 hours after the LH ovulation process. When brain is stimu- release. After ovulation, or rupture of lated by light, it signals anterior pituitary the follicle, the yolk spends approxi- gland to release maturation and ovulation hormones. After maturation and release mately 26 to 28 hours in the oviduct, of an ova, the ovary secretes feedback where various glands secrete the albu- hormones which tell brain it is time for men, membranes, and shell that go to pituitary to reduce its hormone produc- make up the complete egg. tion, thus completing ovulation cycle. It was known that under a normal period of daylight a hen will lay an egg on each of two or more consecutive days, skip a day, and then repeat the pituitary gland had been removed, no cycle. So when a hen has produced an ovulation took place. This made it ap- egg on each of 2 consecutive days, she pear that hormone secretion from the is said to have a two-egg sequence; pituitary was necessary for ovulation. production on 3 consecutive days gives There is considerable evidence that her a three-egg sequence, etc. upon receipt of a light-controlled sig- The hen iisually lays the first egg in nal, nerve terminals of the hypothala- a sequence during the first part of the mus discharge a substance called re- Hghted or daylight period. Within 15 leasing factor into the bloodstream. to 45 minutes after she lays this first This is carried to the pituitary where it egg^ ovulation of the second egg takes stimulates that gland into secreting the place. The time lapse between laying maturation and ovulation hormones. an egg and the succeeding ovulation These hormones travel to the ovary becomes less as the number of eggs in where the ovulation, or luteinizing, a sequence increases. Thus, if a hen hormone (LH) causes rupture of the has a two-egg sequence, the time be- 46 tween eggs is about 2S}i hours. If she Exposure to very high intensity light is on a four-egg sequence, the time for a short period of time has produced between eggs is about 26 j^ hours, and inconclusive results for different re- for a six-egg sequence, about 25}^. searchers. Additional studies of light In longer sequences, the lag time for intensity, as well as types of light, are eggs in the middle of the sequence was needed. less than for the first or last eggs. One Other physical environmental fac- researcher, who observed a group of tors thought to affect ovulation include birds for a complete year, recorded lag temperature, moisture, and diet. More times for various hens that laid two- research has been done on the effect of through 13-egg sequences. He noted these factors upon mammals and other that when the sequence was above 10 birds than with chickens. This is true eggs in length, some of the consecutive also of external psychological factors eggs were produced in less than 24- such as group interaction or the pres- hour intervals. ence of the opposite sex. Ovulation Observations of the time required for cannot be accomplished in some species phases of the reproductive cycle were without some form of stimulation from made on chickens not subjected to any the mate. However, that is not the case unnatural domestic environments. with the domestic hen. Now the scientists set out to find which Much of the work on ovulation has environmental factors affect the ovula- been basic research. Anything as in- tion process. They soon had enough volved as this biological process must evidence to strongly suspect that be thoroughly understood before ap- changes in the amount of light had a plied research projects can be planned. direct bearing on hormone secretion However, from results obtained in by the pituitary gland. For example, some of these experiments, one might changing "night into day"—exposing suggest how commercial poultrymen the birds to light from 6 p.m. to 6 a.m., of the future could benefit. with the rest of the 24 hours in dark- For example, one scientist removed ness—brought about a corresponding the pituitary gland from a group of shift in time of ovulation. chickens so they would not produce One team of researchers found that LH. He then injected each hen with when hens were exposed to constant LH, varying the amount given as well light, they laid eggs at any time during as the time of the injection. Multiple the day or night. However, Dr. Fraps ovulations were produced. The ovi- and his coworkers found that under duct, which normally contains one egg this same system of constant light, the yolk at a time, now had two, and in hens assumed practically the same pat- one bird, three eggs in various stages tern of ovulation and subsequent egg of development. The oviducts appar- laying as they did under the normal ently had no trouble secreting the 14-hour light period. Even though necessary albumen {egg white) and lights in this experiment were on at membranes. However, the uterus, alJ times, the caretaker started his where the shell is added, did not seem chores at a regular time each morning, to function properly after the first egg and the activity of the birds seemed to passed through, thus the subsequent vary with that of the caretaker. By late eggs were soft shelled. afternoon, when he was ready to quit If the specific hormones produced by work, the hens started to settle down, the ovary could be identified, it might as they would do at the end of a nor- be possible to make them synthetically. mally lighted day. This suggests that the This compound could be put in a LH release mechanism may respond to capsule that would be implanted in other environmental rhythms beside the bird's body, designed so as to make light. However, light is still believed the hormones available to the brain at the main factor which contributes to a given rate. They could thus stimulate the time of ovulation. the brain into signaling the pituitary 47 gland to produce its hormones in the which will genetically pass this trait necessary amounts for ovulation for to their offspring. several months. The number of ovula- As scientists continue to find addi- tions could possibly be correlated with tional keys to unlock the many mys- the maximum ability of the hen to teries of the hen's brain, and geneticists, produce a complete egg. nutritionists, and pathologists continue Determining the complete effects to make advances in the poultry field, that various environmental conditions the people of the world hopefully will have on the biological clock in the be assured enough eggs for future needs. brain may make it possible to get all For further reading: ovulations to take place at the same Fraps, Richard M., "Effects of External time each day. This should increase Factors on the Activity of the Ovary." In the the number of eggs in each sequence Ovary II, Sir Solly Zackerman, editor, Academic Press, New York, 1962. and lessen the number of "vacations" "Photoregulation in the Ovulation a hen takes each year. Cycle of the Domestic Hen." Presented at Under a project in progress at Belts- the International Colloquium on Photoregu- ville since 1962, hens are exposed to lation of Reproduction in Birds and Mam- mals, Centre National De La Recherche light for 12 hours and to darkness for Scientifique, Montpellier, France, 1967. 6, creating an 18-hour ''day." This is Nalbandov, A. V., "Mechanisms Control- equivalent to 486 light/dark days a ling Ovulation of Avian and Mammalian year. The scientists are attempting to Follicles." Control oj Ovulation, C. A. Villee, discover if this short day will speed up editor, Pergamon Press, New York, 1961. Opel, H. and Nalbandov, A. V., "Ovula- the ovulation cycle, and whether a bility of Ovarian Follicles in the Hypophy- strain of chickens can be developed sectomized Hen." Endocrinology. Vol. 69.1961.

Faster Growing Trees Are Boon to the South

KEITH W. DORMÁN

Did you ever wonder who and brown paper boxes. So far, they grew the pine trees used for the paper are ahead in the race to create new in those brown bags stacked at super- types of trees and get seed produced market checkout counters? Chances before the squeeze of more people and are they grew on a farm somewhere pulpmills and less land pinches off the in the southern United States. The supply of paper. important question is, will those bags Tree breeders are working not only keep coming when the supermarkets to make a faster growing tree, but one go on increasing at a rapid rate and that can be harvested easily, perhaps the number of people using them by machine, and has little waste in increases even faster? branches and bark. Trees grow fast in Tree breeders at many locations in the South are crossbreeding lots of KEITH w. DORMÁN is a Research Project Leader trees to make certain we do have at the Southeastern Forest Experiment Station, U.S. plenty of paper for those brown bags Forest Service, Asheville, JV.C. 48