X-RAY EFFECTS ON THE GROWTH AND REPRODUCTION OF WHEAT.
Evidences of miiodification and injury to plant parts are numerous in the extensive literature on the effects of x-ray treatment of plants. JOHNSON (2) lists the effects produced on seventy species of flowering plants. Her work with wheat (3) shows that growing material is more strongly affected than non-growing by equal doses of radiation given in the same way. Seedlings from soaked grains given treatments of 1000 r-units and 5000 r-units made less growth in all respects than did controls, but showed inereased tillering. No flowering data were included. SHULL and MITCHELL (4) obtained deleterious effects when unfiltered radiations were used but the use of metallic screens, high voltage, low amperage, and brief exposures giving approximately 100 r-units, resulted in stimulative action on wheat, corn, oats, and sunflower seedlings. Twentyfour-hour-old wheat seedlings were irradiated with doses of x-rays varying from 565 to 13,560 r-units by FRANCIS (1). Retardation of fresh weight and dry weight production by the growing parts of the seedlings and retardation of linear growth of the coleoptile, the leaf, the primary root, and the lateral roots was obtained with all doses and time intervals employed. Respiration was likewise depressed with the exception of those seedlings which had received the smallest dose of radiation (565 r-units) and which were tested 5 or 6 hours after irradiation. The procedure of SHULL and MITCHELL was closely followed in an attempt to obtain further data on the stimulative effects of filtered x-radiation on growth, height, tillering, heading and flowering, green and dry weights, and moisture content of Marquis spring wheat. An attempt to determine the influence of age of seed on response to irradiation was made by the use of two samples of seed; one 57 months old (4 years, 9 months), the other 9 months old. A preliminary trial was made with Fulhio winter wheat. Methods
STIMULATIVE EFFECTS OF X-RAYS ON PLANT GROWTH.
used for clinical diagnosis and therapy. The practical applications of x-rays in medicine and surgery make it necessary to know the effect which x-rays produce upon the living organism. Many investigators have suggested on the basis of general observations that small doses of x-rays may stimulate cellular activity and growth, but convincing proof of such action has been wanting. In more recent years such claims have been discounted in favor of the belief that x-rays are always more or less destructive in action, and tend to retard growth. It is not the purpose of this preliminary report to survey the literature dealing with the effects of x-ray treatments upon plants. It has been found that every part of the plant body can be profoundly modified by appropriate treatments. Cytological and histological examination of treated cells and tissues reveals striking changes in the organization of the protoplasm and of organs derived from the treated meristems. Most frequently the results described are of a destructive nature. The protoplasm is partially disorganized; chromosomes are vacuolated or fragmented; the cell division mechanism functions imperfectly, showing unequal distribution of chromosomes, non-disjunctions, translocation of pieces of chromosomes from one to some other non-homologous chromosome, etc. Gene changes may be produced, often injurious in character, with resulting lethal effects and tendency to sterility. The results obtained by McKay and Goodspeed (5) on cotton are typical. Many mutations have been induced in maize and barley (7, 8), and tobacco (1), but it has been questioned whether there are any progressive evolutionary changes induced by x-ray treatments. All vegetative parts are subject to injury by x-rays. Root tips may become bulbous and swollen, with tumor-like enlargements in which giant cells may occur. Stems become fasciated under strong treatments. Leaves are injured readily ; they become asymmetric and crumpled in appearance, develop deep sinuosities, and often show irregular development of chlorophyll. The sunflower shows these injuries in typical fashion, the leaves becoming pocked and marked as though they were suffering from a mosaic 1 This investigation was aided in part by a grant to the University of Chicago from the Eockefeller Foundation.
EFFECT OF X-IRRADIATION UPON GROWTH AND REPRODUCTION OF TOMATO.
Materials and methods Seven different sets of experiments (series I-VII) were carried on, in most of which the John Baer variety of tomato was used. In the first three series irradiation was carried out when the plants were from 1 to 3 centimeters in height; in the fourth, three medium doses were given at two-week intervals,-at a time when the plants seemed to be recovering from the effects of the previous dose. In the last three groups, the plants were not exposed until small buds had formed. The general procedure was to plant seeds in 5-inch pots in the greenhouse. The plants of the first three series were irradiated before the true foliage leaves had developed. Soon afterwards these seedlings and an equal number of controls were transplanted to larger pots where they grew to maturity. Plants of series V, VI, and VII were transplanted at an early+ age but were not irradiated until small buds had formed. Irradiations of the first five groups were made with a Victor X-ray machine with the following "set-up": 5-inch spark gap, 5 milliamperes current, no filter, distance30 cm., time from 20 to 30 minutes. For the last group, an Acme machine was used with the potential 90 K.V., 5nmilliamperes current, no filter, distance 30 cm., time 20 minutes.