In spite of the war, researches in plant science continued much as usual, at least in the United States; but this was unfortunately not true of the old world countries, where much of the energies and resources were perforce directed elsewhere. In this country the general interest in the effect of chemical substances on plant growth and development continued and a large number of papers along this line appeared. It is, however, impossible, for lack of space, even to name all of the brilliant papers on this and other subjects.
Morphology.
Among notable papers on morphology and anatomy of plants are the first in a series of studies on the phloem of monocotyledons, by Vernon I. Cheadle and Natalie B. Whitford of Rhode Island State College at Kingston, R. I.; on megasporogenesis and embryo-sac development in Calochortus, one of the Liliaceae, by Marion S. Cave, of the University of California, at Berkeley, Calif., on the morphology of Regnellidium diphyllum, by Noe Higinbotham of Columbia University, New York City; on the development of rays in the dicots, by Elso S. Barghoorn, Jr., of Harvard University; on some histogenic features of the shoots of Cryptomeria japonica, by G. L. Cross of the University of Oklahoma, at Norman, Okla.; on fertilization in Vallisneria, by R. B. Wylie of the University of Iowa at Iowa City.
Deficiency in Mineral Elements.
A considerable amount of matter has been published relating to the effect of a deficiency of mineral elements, including the so-called 'trace' or minor or 'micro-elements,' such as boron or zinc, on vegetable crops. In some publications, colored photographs of leaves of various crop plants are presented, showing definite color changes or mottlings which are called 'hunger signs.' These are extreme cases, but they are supported by experimental work. The symptoms under field conditions, on account of the complex nature of the environment, are probably rarely as clearly cut as those depicted.
Hormones.
Vitamin B1.
One of the sensations of the year has been the bursting of the vitamin B1 bubble; which, by-the-way, had grown to a large size. As to the nature of this plant hormone, Dr. G. S. Avery, of Connecticut College, a recognized authority on plant hormones, says that it is 'normally produced in the green tissues of the plant, and is transported to the roots. Root growth, in many species at least, cannot go on without it. If roots are cut off from the parent plant and then grown in a culture medium, vitamin B1, or thiamin, has to be added to the nutrient medium.' Dr. Alvin J. Cox, Chief of the Bureau of Chemistry, Calif. Dept. of Agriculture, says: 'A small amount of vitamin B1 is believed continually required in the life processes of both animals and plants.'
The beginning of the vitamin B1 craze can be traced to an article in one of the magazines on gardening which appeared in October 1939, with the headline as follows:
'News of an exciting discovery ... of five-inch rose buds, daffodils bigger than a salad plate, snapdragons six feet tall, roses transplanted while flowering ... the story of a miracle-working powder and how to use it indoor and outdoor gardening this fall.'
This craze has lasted more than a year, during which time many enterprising floriculturists and seedsmen have fattened their pocketbooks by reason of the alleged miraculous powers attributed to vitamin B1; but at length the credulous public is being quietly disillusioned by sober scientists. Dr. P. W. Zimmerman of Boyce Thompson Institute at Yonkers, N. Y., writes in the American Rose Annual for 1941 as follows:
'The preponderance of evidence from scientists is opposed to the use of vitamin B1 for practical purposes. My own convictions, based on our experience at the Boyce Thompson Institute and the published results of other scientific laboratories, are that vitamin B1 has been badly exploited, and that it has no value as recommended for horticultural practice.'
And a bulletin issued in June 1940 by the State of California Department of Agriculture (Vol. 29, No. 2, pp. 106-109) refuted the claims made for vitamin B1 and showed how the sale of it and the claims made for it in California represented a misdemeanor. The bulletin states:
'As a whole it is believed not proved that the artificial addition of vitamin B1 will produce a beneficial effect on plants, but there are exceptions ... The question of adding vitamin B1 to commercial fertilizers needs a great deal of research before it is undertaken.'
Dr. Zimmerman, in a letter to Dr. J. H. McFarland, printed in the American Rose Magazine for November-December 1941, says ... 'The scientists in general have completely discredited vitamin B1 for practical purposes.' The conclusion of the whole matter is that vitamin B1 is not a miracle worker, but it has been demonstrated that in many species of plants (not in all) roots cannot grow unless it is present in minute amounts. A small amount, also, seems to be necessary for normal metabolism.
Sulfanilamide.
Among the papers presented at the fiftieth anniversary celebration of the University of Chicago was one by Prof. John M. Beal which stated that sulfanilamide produces effects similar to those brought about by colchicine, stopping the process of mitosis or cell division midway, thus causing the formation of extra large cells which double or quadruple the number of chromosomes.
Growth hormones in general have been recently used for producing seedless fruits from unpollinated flowers, e.g., seedless tomatoes and holly berries. Spraying orchard trees with the hormones has had the effect of inducing apple and other trees to hang on to their fruit instead of dropping prematurely, and of hastening the ripening of oranges.
New Sweet Corn.
A wilt-resistant hybrid yellow sweet corn has been developed by E. S. Haber, research horticulturist at Iowa State College. This new hybrid has consistently outyielded Golden Bantam from 60 to 80 per cent, often actually doubling the weight of ears per acre. The new hybrid is resistant to bacterial wilt and to smut, can be grown from coast to coast in the northern United States, and has been grown successfully in Texas, Louisiana and some of the other southern states.
Diseases of Trees.
A new disease of cherry trees called 'vein clearing' causing a loss of green color along the leaf veins and a general mottling of the leaf surfaces, has been described by S. M. Zeller and A. W. Evans of the Oregon Agricultural Experiment Station at Corvallis. Prunes as well as cherries, both important commercial crops in the Pacific Northwest, are attacked. The disease, caused by a virus, transmissible by grafting with diseased stock, has been found also in ornamental flowering cherries, on Italian prunes, and on several species of wild cherry.
Winter Injury.
In the region about New York City, including northern New Jersey and southwestern Connecticut unusual weather conditions resulted in the killing back of thousands of rhododendrons, both native and hybrid forms. A fairly mild period during the early part of March was followed by severe winds with low temperature. This caused the leaves to roll up tightly, dry out; and in more exposed places a large part of the plant or even the whole plant was killed. The rather dry condition of the soil resulting from low rainfall in 1940 was doubtless also a contributing cause of the damage. Mountain laurel (transplanted) was affected to some extent, and later, in April, many of the members of the pine family were affected. The extremely dry weather during 1941, at least in the eastern states, augurs ill for trees and shrubs, for they will enter winter with a dry soil and subsoil and will, therefore, be more susceptible to injuries such as the above. On the other hand the normally drier areas of the midwest have, in 1941, received a marked excess of precipitation.
Dutch Elm Disease.
Several times of late years it has been reported that the spores of the fungus responsible for the Dutch elm disease can be transported lengthwise in the trunk in the vessels or pores of the wood. This is an unusual method, indeed, for dissemination of disease, but it is possible and understandable here because the fungus in question can form spores in the interior of the wood in the vessels themselves. Now Dr. W. M. Banfield of the Division of Forest Pathology, U. S. D. A., stationed at Morristown, N. J., at one of the laboratories for the study of the Dutch elm disease, has removed all doubt about the matter. By field experiments, using the American and slippery elms, he has shown conclusively that the spores are readily transported by the sap stream in the vessels of the wood. As one would suspect, a priori, this movement is rapid during the spring season, averaging more than 44 feet in trees 50 feet in height in from 20 minutes to 48 hours. In the summer the movement is less rapid and extensive, and in the 'non-leafy season' the spores 'could not be recovered at more than 24 inches above injection points.' This method of transport was also found to be true of other wilt producing fungi, namely, Verticillium dahliae and Dothiorella (Cephalosporium) ulmi.
As regards the spread of the disease in the United States there has been but little enlargement of the infected area of 1940. The first occurrence in Massachusetts was reported in 1941 in the town of Alford: other localities where the disease has been found, such as Old Lyme, Conn., Cleveland, and Cincinnati and a few others have had no recurrence of the trouble. This is in marked contrast to the rapidity with which the chestnut blight swept the country.
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