GROWTH MODIFICATIONS IN CITRUS SEEDLINGS GROWN FROM X-RAYED SEED

A summary is made in the present paper of certain morphological variations observed in seedlings of the citrus fruits arising from seed exposed to x-rays before planting. The work has been undertaken in the course of a series of investigations on the biological effects of x-rays and cathode rays, and although as yet no cytological examination of the material has been made, it was considered worth while to assemble descriptions of certain morphological effects at the present time, in view of the paucity of x-ray work reported with the citrus fruits, especially at higher voltages and currents. Certain of the variants considered have already been described,' but have been included here in order to complete the series. Seeds of lemon, lime, tangerine, grapefruit, and sweet and sour orange were obtained through the kindness of Dr. R. G. LARUE, Superintendent of Cultivation of the University of California Agricultural Experiment Station, and Dr. A. F. CAMP, Head of the Department of Horticulture of the University of Florida. They were dried previous to shipment. A portion of the seed was x-rayed in the condition in which it was received. The remainder, before treatment, was soaked in distilled water for 15 minutes, then left in a completely moisture-saturated atmosphere for 12 hours. The seeds were then dried on filter paper and exposed at once. Treated seeds werd planted immediately in seed flats, a mixture of one-third peat moss and two-thirds sharp sand being used, the seeds being covered in most cases with pure sharp sand. The seeds were germinated in an electrically heated greenhouse, day temperatures being maintained constant at 750 F. and night temperatures at 550 F. during the early growth of the plants. At a later time a large number of apparently normal seedlings were transferred to the open nursery, being planted in a sandy loam soil. Most of the more conspicuous variants were maintained in the greenhouse for a full year, however, being transferred to benches containing a mixture of sand, clay, and manure at the age of a few months. After this change they were not disturbed until the close of the experiment. A Coolidge water-cooled tungsten-target tube of the thick-walled type was used as the source of x-rays, operated at 200 k.v.p. and 30 ma. from a Science, Aug. 5, 1932. Science, Feb. 15, 1933. Bot. Gaz. 94: 801-807. 1933.