1940: Botany

A review of the 1940 researches in plant life must take into account the disastrous influences of the widespread European war, and of the wars in the Far-East. In Europe and in Japan, as is to be expected, research was curtailed and correspondence between scientists in these countries and America was difficult or impossible. Subscriptions to our American botanical magazines in many cases were terminated, resulting in a diminution of funds available for publications here. Chronica Botanica, formerly published in Holland, has been transferred to the New World, and is now published in Waltham, Mass. Published weekly, it 'gathers all scientific, professional, and personal news and comments which may help plant scientists (now over 80,000 in about 4,000 institutions) with their current work and new projects.'

The herbaria of the department of botany of the British Museum, together with original drawings, manuscripts and valuable books, have been moved and stored in such a way that they will be as safe as possible, but still may be consulted if necessary.

The herbarium of the Musée d'Histoire Naturelle, Paris, which after the outbreak of the war was divided among three castles near Paris for safe keeping, is in good condition and has been returned to the Musée.

Here in the United States plant research in the hundreds of institutions — state experiment stations, college and university departments, botanical gardens, and private foundations has gone forward as usual, resulting in a host of scientific papers of outstanding merit, of which there is space here to outline only a few.

As in recent years, a large number of researches deal with problems in plant physiology and particularly with the effect of chemical substances, plant extracts, etc., on plant life and development. Many notable papers on morphology have appeared, such as that by A. S. Foster of the University of California at Berkeley, on the shoot apex of Cycas revoluta; by J. T. Buchholz of the University of Illinois, on the embryogeny of Torreya; and by Fred T. Wolf of Vanderbilt University, Nashville, Tenn., on the development of the female gametophyte in Yucca aloifolia. Valuable taxonomic papers have appeared such as: the Oscillatoriaceae of Virginia by J. C. Strickland of the Miller School of Biology, University of Virginia at Charlottesville, Va.; plants from northern South America by A. C. Smith, of the New York Botanical Garden, to name only two of many notable papers in this field. Albert H. Tillson of the Division of Plant Exploration and Instruction, Bureau of Plant Industry, U. S. Dept. of Agriculture, finds in a study of the subfamily Kalanchoideae of the Crassulaceae that on the basis of their vascular anatomy in the floral region, Bryophyllum and Kitchingia are valid genera, but that Kalanchoe Fedtschenkoi, K. Gastonis-Bonnieri, and K. Waldheimi are really species of Bryophyllum. (See also HORTICULTURE.)

Photoperiodism.

The striking researches of H. A. Allard and W. W. Garner of the Bureau of Plant Industry, on the response of plants to the relative length of daylight were published in 1920 and 1923. Before the work of those investigators the fact that the relative length of day is really a dominant factor in plant reproduction seems not to have been suspected. They found that certain plants (short day plants) flowered under the influence of short daylight periods, thus in the early spring or in the fall; while other species (long day plants) bloomed under the influence of long days, i.e., during the summer. They found, too, that short day plants exposed to longer illumination each day by artificial means would flower tardily or not at all. The same was generally true of long day plants, exposed to shorter light periods than those to which they were accustomed. In a publication of the Bureau of Plant Industry this year they give the results of further experiments in this field, extended to both wild and cultivated plants. For example, most of the asters, which bloom naturally in the fall, are short day plants. However, if their period of illumination is artificially shortened earlier in the season, they may be brought into flower in June or early July. On the other hand, long day plants, such as Gladiolus gandavensis and Iris florentina, may have their flowering inhibited by shortening their exposure to light to 12 hours a day. Further, some plants, such as the wild Polygonum pennsylvanicum, are apparently indifferent to the length of daylight in so far as its effect on their flowering period is concerned. Practical applications of this remarkable discovery are, e.g., the practice of chrysanthemum growers in forcing their crops into earlier flowering by the use of black cloth to shorten the daylight period. Electric light has been used to supplement short days for the China aster (a long day plant) thus forcing the plants into earlier flowering.

Fungi.

W. J. Robbins, working at the New York Botanical Garden and at Columbia University, finds that extracts of the mycelium of Phycomyces favorably affect the germination of its spores, and at least the early growth of its mycelium, cultivated in a medium of minerals, sugar, asparagine, and thiamin. Extracts of mycelia of various ages increase in effectiveness with the age of the mycelium, and then decrease, showing some correlation with the rate of growth of the mycelium from which the extracts were prepared.

G. M. Watkins and Matilde Otero Watkins of the Texas Agricultural Experiment Station in a study of the pathogenic action of Phymatotrichum omnivorum, the fungus responsible for a root rot of the cotton plant, conclude that exudates from the mycelium of this fungus contain thermolabile substances, probably enzymes, which are largely responsible for the destruction of host cell walls during infection. This is quite in line with the action of many so-called parasitic fungi, which kill the cell before they invade it.

An important contribution to our knowledge of parasitism in fungi was the discovery, by G. M. Reed in 1924, of physiologic races of oat smuts. Working at the Brooklyn Botanic Garden, Reed found that certain smuts, although apparently identical in outward appearance, manifested a differential behavior when applied to certain varieties of oats, that is, a smut (Ustilago levis) from Wales when applied to Avena brevis (a variety of oats) infected it, but gave practically negative results on Avena sativa. On the other hand, what was apparently (morphologically) the same smut, collected at Columbia, Missouri, infected Avena brevis only slightly, but attacked several varieties of Avena sativa. In other words, two fungi, although apparently of the same species, may not possess the same internal propensities — somewhat as in the case of human twins, apparently identical, but one with a good and the other with a mean disposition. Now Reed comes forward with a new paper in which he announces (in all) 'twenty-nine physiologic races of Ustilago avenae and 14 of U. levis differentiated on the basis of their behavior on definite strains and varieties of nine species of oats.'

Diseases of Trees.

The Ceratostomella disease of the plane tree has recently been reported by Paul V. Mook, of the division of Forest Pathology, U. S. Department of Agriculture, as affecting considerable numbers of London planes (Platanus acerifolia) near Wilmington, Delaware, where a number of trees are already dead. Also, at Knoxville, Tenn., a large American plane or sycamore (P. occidentalis), and at Middlesboro, Kentucky, two American planes were found in advanced stages of the disease. Ceratostomella, the causal fungus, produces a 'bluish black, moist-appearing wood discoloration,' which is the principal internal symptom. Authentic reports of this apparently new disease have come previously from Pennsylvania, Maryland, New Jersey, and the District of Columbia. The London plane is a tree admirably adapted to succeed in large cities on account of its tolerance of dust, smoke and gases, and drought. But, in view of these reports, city authorities should await further developments before making extensive plantations of this species.

As to the Dutch Elm disease, a slight increase of the infection area has been reported, but nothing at all comparable to the rapid spread of the chestnut bark disease, which has now killed off practically all our large chestnut timber trees.