978 BIOLOGICAL EFFECTS OF RADIATION 



histological studies of X-rayed tissues should be made in order to better 

 understand the real effects of the rays upon developing tissues. 



SUMMARY 



Investigators who have reported morphological and histological 

 changes in treated plants have emphasized irregularities in leaf appear- 

 ance, anomalies in shape and margins, variegations in leaf colors, includ- 

 ing the appearance of chimeras. They have found that increased 

 development of aerial as well as underground stems is of common occur- 

 rence in ray-susceptible plants while fasciations of stem and flower heads 

 have been reported for a few species. Raying of budded plants seems 

 to cause abscission of many buds; those which do bloom and develop 

 fruits are usually abnormal and the fruits mature with a decreased 

 number of seeds. Histological studies indicate the stems of treated 

 plants show an early development of xylem made at the expense of the 

 pith. 



CYTOLOGICAL EFFECTS OF X-RADIATION 



Lopriore (37), in 1898, found that treatment of Vallisneria spiralis 

 produced an acceleration of protoplasmic streaming which was checked 

 by longer exposure. Seckt (59) reported that exposure to X-rays 

 distinctly favored the streaming movement of protoplasm of Mimosa 

 and Oxalis. Williams (69), working with strips from the upper surface 

 of the petiole of Saxifraga umbrosa, found that the circulation of cyto- 

 plasm was first accelerated by small doses of the rays, but that depression 

 followed and there was no return to normal. There was evidence of a 

 lowering of viscosity of protoplasm in the early stages of radiation. 

 Weber (67), on the contrary, reported that in living plant cytoplasm no 

 viscosity changes appeared as primary effects of the rays. Vintemberger 

 (65) has shown that the protoplasm resists the action of the rays, or if 

 injured by their passage, it is quickly repaired under the influence of 

 the nucleus. The selective action of the rays is on the nucleus and 

 chromatin. 



The work of Jiingling and Langendorff (24) indicates that small 

 doses which do not cause visible harm to the root tips of V. Faha make a 

 change in the rhythm of nuclear division. A curve constructed to show 

 the number of mitoses in unrayed root tips during a period of 24 hr. has 

 but a single peak and is somewhat symmetrical. The maximum number 

 of mitoses occur during the day; the minimum, at night. A similar daily 

 rhythm in nuclear division of root tips has been found in the pea. After 

 irradiation with a relatively light dose of X-rays, not 1 maximum but 

 2 maxima occurred within 24 hr. A curve showing 3 maxima was evident 

 when the dose was doubled. Retardation of growth was manifest and the 

 number of defective divisions increased with heavy doses. With a dose 



