Investigations in plant science during 1939 succeeded in many fields in pushing still farther back the film that divides the known from the unknown. Biological Abstracts, the journal which contains the gist of biological papers published from month to month throughout the scientific world, and which was threatened with collapse in 1937, has now been placed on an even keel. It is reported that in 1939 this journal published abstracts of 18,108 papers, as against 16,323 in 1938. In October 1938, 575 scientific journals were covered, but in October 1939, that number was raised to 1,113.
It is of course impossible in limited space to review in detail this vast amount of material. It is possible to select only certain pieces of research which seem valuable either from the point of view of pure science or important from an economic standpoint; and meanwhile to indicate the general trend of thought in plant science. Much that is doubtless of equal importance must be omitted.
Hydroponics.
The rage for growing plants by the water-culture method, i.e., by adding the requisite mineral elements in solution to the water in which the roots of a plant are immersed, continues unabated. It is an old idea — not really new knowledge — but because of much advertising it has caught the popular fancy. School children are trying it; enthusiastic, budding scientists have chosen it for a hobby. In so far as it propagates a knowledge of 'how plants grow' it is good. The only way in which it can possibly claim an advance in our scientific knowledge is its application on a commercial scale to growing large crops. But on this point, D. I. Arnon and D. R. Hoagland, of the College of Agriculture, University of California, declare:
'It must be clearly recognized that the application of the water-culture method for crop production will be limited primarily by economic considerations. . . . It seems highly improbable, in view of the present cost of a commercial water-culture installation and its operation, that crops grown by this method could compete with cheap field-grown crops. In greenhouses specializing in high-priced, out-of-season crops the method appears to have commercial possibilities. The expense of growing greenhouse crops in soil, including cost of equipment for sterilizing soils, may frequently stand comparison with the cost of growing crops by the water-culture method. . . . The suggestion that important amounts of food could be produced economically in small-scale installations for home use has no sound basis, because of high costs of the installations and technical requirements for the successful use of the method.'
Hormones.
Hormones, i.e., substances which bring about specific physiological reactions, are generally held to include the auxins and are divided by Huxley (1935) into 2 groups: A, regional activators and B, distance activators. J. R. Raper of Harvard University, in a study of the sexual relationships of Achlya, one of the water molds, concludes that several hormones operate here in the formation of sexual organs. James Bonner and Philip S. Devirian, of the William G. Kerekhoff Laboratories of the Biological Sciences, California Institute of Technology at Pasadena, Calif., find that isolated pea roots can be cultivated indefinitely in nutrient media containing vitamin B1 and nicotinic acid, in addition to mineral salts and 4 per cent sucrose. But substances requisite for growth vary with different species. In flax roots, for example, vitamin B1 is the only accessory growth factor required.
W. J. Robbins, of the New York Botanical Garden, has shown (1938) that some fungi are able to synthesize a growth substance (vitamin B1) known as thiamin, provided they are supplied with the necessary chemical elements. He now finds that other fungi, which are heterotrophic, i.e., unable to synthesize this growth substance, will thrive when in the proximity of fungi autotrophic for thiamin, and suggests 'possible nutritional relationships between symbionts and between parasite and host, other than those involving carbohydrate and nitrogen compounds hitherto commonly assumed.'
Cellulose.
Cellulose (C6H10O5)n, an organic substance peculiar to plant life, has become indispensable to our civilization. Cotton is almost pure cellulose, and, in a slightly altered chemical state, cellulose forms the basis of wood. Closely related to starch (C6H10O5)n, and sugar, it forms the chief structure of the membranous cell-walls of plants, and is permeable to watery solutions. Just how and where it forms have always been a mystery. Now Dr. Wanda K. Farr of the Boyce Thompson Institute at Yonkers, N. Y., finds that it is formed within the plastids (disc-like bodies) in the plant cell. At least this is true of the alga Halicystis, and also of the cotton plant. It originates as small, ringlike structures inside the plastid, which grow until the membrane of the plastid breaks down. The rings are then released and subsequently break up into cellulose particles. The particles are of the same size, since the rings are of the same thickness, throughout. It appears reasonable to assume that the cellulose is formed in the plastid directly from the photosynthetic sugar.
As to the way the cell wall is built up, I. W. Bailey, of Harvard University, suggests that the cellulose matrix 'is composed, in the submicroscopic field, of aggregations of chain molecules that are held together by overlapping chain molecules. In the microscopically visible field, it is constituted of coalesced microfibrils. In both fields of magnitude, the continuous cellulosic system is perforated by a continuous system of interconnecting capillary spaces.'
Tissue-culture Experiments.
Philip R. White, of the Rockefeller Institute for Medical Research at Princeton, N. J., has carried small cones of tissue taken from near the stem tip of a hybrid Nicotiana in a living and growing condition in nutrient agar cultures for 40 weeks without evident differentiation, and apparently with unlimited capacity for growth. This was in a semi-solid (agar) medium. However, after transfer to a liquid medium, differentiation began to take place, growing points and even small leaves forming, showing that the 'cell groups were nearly if not completely totipotent.' He suggests that the difference in oxygen conditions may produce these different results.
Morphology.
J. T. Buchholz, of the University of Illinois, presents a careful study of the morphology and embryology of Sequoia gigantea, the 'Big Tree.' He finds that in its development the female gametophyte follows the usual program observed in other conifers, in its embryogeny resembling most closely that of Sciadopitys. In a later paper, in which he presents a similar study of Sequoia sempervirens, the Redwood, he finds sufficient differences between these two species (as they are now classed) to warrant their being placed in separate genera.
From ontogenetic studies of flower buds, A. Gundersen, of the Brooklyn Botanic Garden, finds that parietal placentation is the earlier condition; for those flowers with axile placentation usually have, in the beginning, parietal placentation, i.e., in the bud stages. He believes, therefore, that in a natural classification, groups such as the Opuntiales, Parietales and Papaverales should be placed together early in the system.
Plant Diseases.
P. R. Miller, of the Division of Mycology and Disease Survey of the Bureau of Plant Industry, U. S. Department of Agriculture, finds that in the Apple-rust—Cedar-apple disease, in which the casual fungus Gymnosporangium juniperi-virginianae lives alternately on apple and species of Juniperus, the aeciospores from the fungus on the apple infect Juniperus at two fairly distinct periods, first toward the end of the summer, and second (and more commonly) in early spring. Fungicides applied to Juniperus during the winter should therefore be effective in the control of the disease. O. C. Anderson, in a study of the blister-rust-resistant Viking red currant, finds that the resistance to infection is 'physiological rather than physical'; i.e., there seems to be some protoplasmic incompatibility which prevents the growth of the fungus in the host cells.
Dutch Elm Disease.
From Jan. 1 to Sept. 9, it was found that 10,246 trees were affected with the Dutch Elm Disease — most of them (8,438) in New Jersey. Several new counties in New York State and New Jersey have been added to its range. Apparently the disease is spreading, though very slowly, in spite of the determined efforts of the U.S.D.A. to eradicate it. See also BIOLOGY; HORTICULTURE.
Paleobotany.
See GEOLOGY.
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