1940: Biology

Plant Life.

Influence of Oxygen and Growth of Plant Tissue.

That oxygen abundance or lack determines the character of growth masses of plant tissue in a culture medium, has been shown by Dr. Philip White, of the Rockefeller Institute for Medical Research at Princeton, N. J. He found that if these tissues received a sufficient supply of oxygen they would continue to grow but the cells would not differentiate. However, when oxygen starvation was intensified the undifferentiated mass of tissue proceeded to produce small leaves, supported on small stems.

Carbon Dioxide Absorption and Use.

Dr. H. Gaffron of the University of Chicago has reported experiments where one-celled green water plants would absorb carbon dioxide in the dark. Previously, Dr. Gaffron had reported the ability of these plants to combine oxygen and hydrogen, presumably with the release of energy for their own use in dim light. Now in later experiments he finds that if a small amount of carbon dioxide is added to the artificial atmosphere a part of the carbon dioxide will be absorbed by the plant in the absence of light.

Another case of unorthodox use of carbon dioxide was recently reported by Prof. S. O. Mast of Johns Hopkins University. He found that a protozoan or one-celled water organism known specifically as Chilomonas paramecium could manufacture food substances, such as starch and fat, without chlorophyll and in the absence of light. And further than that, he found this organism could produce food and reproduce and grow in a solution containing only inorganic materials. This is probably the first time an organism, which is usually considered in the animal kingdom, has shown the ability to do a plant's work and manufacture food out of the inorganic substances especially without the commonly excepted substance chlorophyll. These two experiments on plant and animal forms will no doubt necessitate a revision of the accepted ideas regarding photosynthesis or the processes of food formation and energy liberation.

Effect of Colchicine on Plant Genetics.

In the field of plant genetics the drug colchicine has been used to carry out more interesting experiments. Drs. H. E. Warmke and A. F. Blakeslee of the Carnegie Institution of Washington have reported profound sex changes in an Old-World species of plant known as Melandrium dioicum when this plant is treated with colchicine. New strains with double the number of chromosomes have been produced. Furthermore, they have produced a strain which has male and female (pollen and seed-producing) parts in the same flowers. This is a profound change since this plant in nature bears male and female flowers on separate plants.

Other possibilities as the result of plant treatment with this drug colchicine have been carried on experimentally by Drs. B. R. and M. R. Nebel at the New York State Agricultural Experiment Station. They have also artificially produced plant cells with increased chromosome numbers and hence, have produced marigolds, snapdragons, and other species of flowering plants which have entirely different genetic properties from those of the original species.

Vitamins in Relation to Plant Growth.

Experiments with vitamins in relation to plant growth have been continued and in the experiments carried out by Dr. R. Denison of the State University of Iowa, two vitamins necessary for human health have been shown to stimulate plant growth. In these experiments it was found that riboflavin, one of the B vitamins, enabled the eggplant to develop longer stems with heavier tops and the leaves were coarser in texture and darker in color than the untreated plants. Vitamin C or ascorbic acid was shown to have caused unusual gains in the size of the tobacco leaf also.

Unicellular Organisms.

Social Behavior in Unicellular Organisms.

Professor H. S. Jennings of the University of California at Los Angeles has made a comprehensive study of the social behavior in unicellular organisms. He has found that the sex drive or the urge to find a mate which is so common and well recognized in higher organisms is found also at the very bottom of the evolutionary scale. This does not mean that the small unicellular organism is as highly developed socially as higher animals, including man. Professor Jennings explains this by stating that the unicellular organism, such as the Paramecium, reacts without any awareness of the action or its relations. Man and higher organisms operate on a social scale wherein the awareness of the action is present and often times consciously planned.

Effect of Nucleus Removal in One-Celled Animal.

Professor Vance Tartar and Dr. Tze-Tuan Chen, in researches conducted at Yale University and the University of California at Los Angeles, have shown that the one-celled animal, Paramecium, can go through characteristic mating reactions even though the nucleus has been removed. This is most remarkable, since the nucleus of a cell has usually been considered as the controlling center for most physiological activities.

Animal Life.

Influence of Environmental Variation on Invertebrate Survival.

Professor D. M. Whitaker of Stanford University has shown that the brine shrimp Artemia, an invertebrate species, has the ability to withstand remarkable environmental variations. He found that this species, when in the embryonic or encysted state, could survive when scaled in a glass tube under vacuum and hence without oxygen for six months at least. Other embryos were able to develop normally after a 24-hour immersion in liquid air, at a temperature of 310 degrees below zero.

Color Changes in Animals.

Professor G. H. Parker of Harvard University states that the common catfish can change its color in much the same manner as the chameleon lizard. However, the only difference seems to be the time required. The catfish changes its colors much more slowly. Doctor Parker has carried out extensive experiments on pigmentation in various forms of animals and more recently has discussed the physiological mechanism of these color changes. In general, he suggests that secretions, as the result of glandular reactions, are probably involved. The pituitary liberates intermedin and the nerves secrete a substance (probably acetylcholine); these two are the substances which darken the skin while the hormone which contracts the pigment and lightens the skin is probably adrenalin from the adrenal glands.

Sex Reversal in Fish.

Drs. F. M. Baldwin and H. S. Goldin of the University of Southern California have performed experiments on sex reversal in fish, changing females into males by the injection of synthetic male sex hormones.

Embryonic Membranes of Fishes.

Dr. C. L. Turner of Northwestern University has described embryonic membranes in several higher species of fish. These species give birth to their young alive instead of laying their eggs in the water. The membranes which surround the embryos prior to birth are different in detailed structure and function but do resemble similar membranes in higher warm-blooded animals.

Method of Cobra Venom Ejection.

Mr. C. M. Bogert of the American Museum of Natural History has carried out some interesting researches to show, on the basis of experimental evidence, that there are several species of cobras that actually throw or eject their venom straight forward from their mouth. Heretofore, it has been thought that the venom elaborated by these snakes was ejected from the mouth by expulsion of air simultaneously with the dropping of venom into the mouth cavity. Hence the name 'Spitting Cobra.' The experiments of Mr. Bogert show that the venom of these species can be forced out of the fangs directly ahead because of the anterior position of the openings of their fangs.

Technique for the Study of Chick Embryos.

The development of chick embryos can be observed and subjected to experimental procedures by means of a modified technique of making windows in the shells during incubation. This technique has recently been perfected by Professor J. W. Price and E. V. Fowler of Ohio State University. Their technique was simply the removal of a portion of the shell in the large end of the egg and the replacement of a larger shell cap over the open end. The eggs could then be placed upright in the incubator and the cap removed from time to time for observation. This technique is much simpler than that reported by the writer and others but no doubt lends itself more easily to bacterial infection.

Colchicine in Genetic Studies in Animals.

The drug colchicine has been of extraordinary value to plant physiologists in producing genetic varieties but this same drug does not lend itself to animal experimentation along hereditary lines with the same degree of success. Drs. H. A. Davenport and F. B. Queen of Northwestern University recently reported experiments attempting to modify the heredity of rats with colchicine. Their chief difficulty seemed to be the high toxicity of this drug to animal tissues as compared to plant tissues. In concentrations high enough to be effective, the drug caused local necrosis of the tissues in the injected area, while in low concentrations no hereditary effect was noted. These workers suggest the most hopeful possibility for the use of this drug in the genetical studies of animals will probably be the injection of low concentrations directly into the sex organs and in this way modify indirectly some of the hereditary characteristics.

Viruses.

Viruses, best known as causing diseases like infantile paralysis and influenza, may some day reveal the secret of the origin of life. Each year more advances are being made in the study of the nature of these substances. This year Drs. G. A. Kausche and Ruska of the Siemens-Halske laboratory in Berlin were able to demonstrate in photographs with the electron microscope the plant virus which attacks the green chlorophyll particles of leaves. See also ENTOMOLOGY; ZOOLOGY.