970 BIOLOGICAL EFFECTS OF RADIATION 



CONDITIONS AFFECTING RAY-SENSITIVITY OF PLANTS 



Plants on the whole are much more resistant to X-rays than are 

 animals or human beings. Some species show a natural resistance to 

 radiation while others are easily affected. Komuro (28, 30), using a 

 heavy dose of 155 H on V. Faha seeds before planting them in the soil, 

 found that although shoots did not appear above the ground, they 

 developed to a certain extent. He believed it very probable that 

 strongly irradiated seeds are particularly affected in the plumule and 

 radicle; the metabolism of these parts may be so gradually modified 

 that at a certain stage the seedlings may cease to develop at all. John- 

 son (19) found that irradiation of soaked sunflower seeds with a very 

 heavy dose (30 E.) did not kill the embryos, but that the seedlings died 

 soon after the cotyledons appeared above the soil. 



Russ (55) as early as 1919 declared that the effects of radiation are 

 selective; a dose which will destroy one type of cell may be without 

 effect upon cells of a different variety. 



Jiingling (23), a year later, called attention to the fact that sensitivity 

 to radiation varies with different species of plants and that sensitivity 

 depends on the condition of development. Koernicke (27), in 1915, 

 wrote that roentgen culture would not be of practical value in agriculture 

 because of variations in effect among different species of plants as well 

 as variations among individual seeds in the same species. Others 

 (20, 22, 23, 27, 35) also have noted that not only do different species 

 react differently to the same dose, but members of the same species 

 react differently according to individual variation of the seeds and to 

 the stage of development. 



Goodspeed (12) found no dosage which would prevent germination 

 and growth of tobacco. Seeds exposed continuously for 3 hr. to 50 kv. 

 and 5 ma. at a distance of 20 cm, without filters gave, at the end of three 

 weeks, a total germination of over 95 per cent. The initial rate of 

 germination, however, was retarded. This was mainly a transient effect, 

 however, and so far as size and vigor at maturity were concerned, no 

 general effects of X-radiation could be seen. Goodspeed found that the 

 mortality after treatment of seeds which have just broken the seed 

 coat was very high, and that the plants which survived were usually 

 abnormal throughout or obviously reflected a mosaic of nuclear elements 

 within. When germinating seeds or seedlings of tobacco in the coty- 

 ledonous stage were radiated, there was no difficulty in producing lethal 

 effects. Those plants which survived exhibited a permanent as well 

 as a transient distinction in growth and form. 



Iven (17), who delayed planting irradiated seeds for eight months, 

 found that the same effects were manifest as in those which were sowed 

 immediately. Ancel (2a), on the contrary, found that allowing time 



