X-RAY EFFECTS ON GREEN PLANTS 979 



so heavy that 90 per cent of the roots were dead after 14 days, the follow- 

 ing occurred: after 1 hr., the mitosis number showed a 1 per cent increase 

 which was followed by a rapid decrease; after 18 hr., a zero point was 

 reached where no division occurred for 6 hr.; after 60 hr., a second peak 

 was reached followed by a minimum at the 85th hour; the third and 

 smaller maximum was evident at 96 hr., with the third minimum at 

 144 hr. ; a flattening out of the curve then occurred. In general, it may 

 be stated that for successively higher doses, there occur increasingly 

 longer periods devoid of mitoses. 



A mitotic decrease 3 hr. after irradiation with almost complete 

 cessation after 3 days was reported by Wigoder and Patten (70). Cell 

 division was resumed after 5 to 8 days when many abnormal, multi- 

 nucleate cells were observed. 



Nakagawa (44) reported rare occurrence of mitosis after irradiation 

 of sprouted V. Faha seeds. He found it occurring only in the growing 

 point where multinucleate giant cells appeared 45 hr. after irradiation. 



Mitotic irregularities occur also in leaves of X-rayed plants. Dis- 

 placement and replacement of tissues may be going on constantly to 

 produce leaves irregular in form with puckered and roughened surfaces. 

 Goodspeed (12) suggests that in tobacco leaves "the nucleo-cytoplasm 

 ratio has apparently been altered, perhaps as a result of some induced 

 inhibition of mitosis without decrease in the growth capacity of the 

 protoplast." 



Komuro (29), in 1922, from his studies on V. Faha, concluded that 

 heavy doses of X-rays upon the seeds cause an abnormal condition in 

 cells of the radicle. In preparations which Komuro (32) made of root 

 tips of V. Faha, 13^ hr. after an irradiation of 1 hr., vacuolization of 

 cytoplasm was apparent and all observed mitoses were abnormal. Nine 

 hours after irradiation, binucleate cells, giant nuclei, and multinucleolar 

 nuclei were found. He (31) later confirmed his earlier results and 

 reported additional degenerative phenomena occurring in roots of 

 V. Faha: irregular distribution of chromosomes, change in form and 

 contents of the nucleus; appearance of multinucleate cells; a tearing 

 away of the protoplast from the cell wall; vacuolization of both nucleolus 

 and cytoplasm; dissolution of cell nucleus; thickening by contraction of 

 the nucleus such as occurs during the degeneration of a cell. He writes: 

 "It may safely be said that irradiation of X-rays upon the seeds, seedlings, 

 and young plants of Vicia Faha leads the cells of the vigorous growing 

 plant to a diseased or senescent condition resembling that of malignant 

 tumor cells and then to the end of cell life." The soft rays exert a 

 much stronger physiological and cytological effect than do the hard 

 rays, according to Komuro (33). In young plants, cytological alterations 

 take place immediately after treatment with soft rays; in case of hard 

 rays, several hours later. 



