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
Radiation Studies in Eleusine coracana (L.) Gaertn
The material irradiated was the dry dormant seed of Elesine coracana (L.) Gaer tn., the "finger millet". The irradiations were carried out at the M. R. C. unit, Hammersmith Hospital, London, by Mr. Don Moore. The standard glass dish of 3cm diameter receives a uniform distribution of irradiation; over the bottom of this a single layer composed of approximately 300 seeds was placed; they therefore were all equally exposed. After the irradiation the seeds were brought back into the laboratory; half were germinated and grown on in sterile soil, and the other half germinated on filter paper for use in cytological studies. ƒÀ-rays (accelerated electrons) from the Van de Graaf apparatus were used.
GROWTH AND GERMINATION OF SUNFLOWERS AS INFLUENCED BY X‐RAYS
The manner in which the germination and growth of seeds are influenced by X-rays is a subject about which there is disagreement. The question to be determined is whether the action of X-rays on seeds and seedlings causes growth to be stimulated or inhibited. Is the effect on plants merely a transitory one or do the rays also exert an influence on the total amount of growth? In the experiments to be described a considerable number of plants were grown to maturity, so that the final, as well as the immediate, effects of irradiation could be determined. A few of those who have studied the effects of X-rays on higher plants (I, 7, io) report a positive stimulation by weak irradiation and find an acceleration of growth. One investigator (12) finds that X-rays exert a forcing action on certain buds while others (3, 6, 7) find a temporary checking of growth followed by an acceleration. The facts reported in this paper suggest that plants from irradiated seeds show no increase in total growth either at an early or a later stage. The effect of the same dosage on air-dry and soaked seeds is discussed, as is also the variability of seeds of the same species in regard to their susceptibility to X-rays. MOISTURE INTAKE OF SEEDS