of behavior: cells of the growing point of the 

 root and stem are more sensitive than cells of 

 the permanent tissues. 



Ancel (1927) finds the work of many authors 

 who point out differences in the sensitivity of 

 dry and sprouting seeds to be defective because 

 they failed to follow up their studies after the 

 appearance of shoots. She finds it necessary to 

 fill out their experiments in this direction by a 

 study of changes in the sensitivity of lentil seed- 

 lings from the moment that sprouting begins to 

 the time the roots reach a length of 24 milli- 

 meters. Her observations showed that the 

 sensitivity of lentil seeds continued to rise from 

 the moment of the appearance of sprouts, and 

 that it reached its maximum when the roots were 

 10 millimeters long, after which it went down 

 gradually to the time the roots were 24 milli- 

 meters. These results safeguard experimenters 

 from mistakes, if they set up experiments with 

 seedlings whose roots have different lengths. 



Stadler (1928) was the first to show that with 

 equal doses 8 times as many mutations appear 

 in sprouting seeds as in resting seeds. Muta- 

 bility in generative cells at the time of forma- 

 tion of sex cells or reproductive organs was 

 studied in greater detail. 



Goodspeed (1929) pointed out that certain 

 stages of meiosis are particularly favorable for 

 obtaining chromosomal aberrants, but whether 

 the same can be said in relation to gene muta- 

 tions has not yet been determined. 



Stubbe (1932*) showed that when snapdragon 

 buds are irradiated by equal doses more muta- 

 tions occur if the irradiation takes place after 

 meiosis than if it takes place during or before it. 



In Chapter 1 the results of the experiments 

 of Breslavets and her co-workers concerning the 

 variable sensitivity of soaked seeds and sprouts 

 of rye were presented (Breslavets, Afanas'eva, 

 and Medvedeva, 1935)^ and also of dry and 

 soaked seeds of peas ([Breslavets and] Atabe- 

 kova, 1935). 3 



Johnson performed many experiments for the 

 purpose of clarifying physiological changes of 

 plants due to the influence of X rays. Two of 

 her works have a direct bearing on our subject. 

 In the first of these works (1933), 3 the author 

 investigated the effect of irradiation on three 

 varieties of French spinach (Atriplex hortensis): 

 1) the variety with pale, almost yellow leaves, 

 the spinach most frequently used as food, 2) the 

 variety with dark red leaves, which is cultivated 

 as an ornamental plant, and 3) the green variety, 

 which exhibits the most vigorous growth. Ex- 

 periments with different varieties of the same 



species were undertaken in order to determine 

 whether or not the difference in their responses 

 to an external factor (in this case X rays) stems 

 from the physiological properties of the plants 

 themselves — specifically, whether or not the 

 presence of the colored cell sap of [A.] hortensis 

 can protect the protoplasm from the~harmful 

 effect of the rays. Comparative examination 

 revealed that after exposure to X rays all three 

 varieties manifested a significantly smaller 

 size at maturity and a certain retardation in 

 flowering; these responses were strongest in 

 the red variety. In general, the red and pale 

 varieties show greater injury than the green 

 variety. After irradiation the pale plants had a 

 greater percentage of stem lesions and dichoto- 

 mous branching; the green variety had the 

 greatest number of plants with abnormal leaves, 

 altered phyllotaxy, and flattened stems; the red 

 variety exhibited lateral branching more fre- 

 quently than did the others. On the basis of this 

 experiment the author concludes that not only 

 families, genera, and species, but even varie- 

 ties of a single species can differ in their phys- 

 iological and morphological responses to 

 irradiation. 



In her 1936 paper Johnson states that the 10- 

 year investigation of the effect of X rays on 

 various species of plants makes it possible to 

 divide the plants into groups according to their 

 sensitivity to X rays. She divides the plants 

 that had been investigated into: 1) species that 

 are not affected by the radiation, 2) species on 

 which irradiation has a weak effect, apparently 

 only for a short time after irradiation, and 3) 

 species that are sensitive to irradiation. 

 Species of the second group manifest sensitivity 

 to X rays in the early stages of development, 

 but as they mature they resume their normal 

 characteristics. In this group are found: 

 Chenopodium album, Spinacia oleracea, Cheir- 

 anthus, Matthiola bicornis, Calandrinia grand! - 

 flora, Quamoclit coccinea , Asperula orientalis, 

 Portula"ca^ In the third group, a dos e of 2500 r 

 is lethal for seedlings of Nemophila insignis , 

 Gaillardia picta, and Phlox drummondii . For 

 other species of this group a dose of 2500 r 

 diminishes the average size, but out of 39 

 species, 9 show an increase in height. Dimor - 

 photheca increases its average height, while 

 this dose proved to be lethal for many speci - 

 mens of Clarkia, but those which survived were 

 exceptionally strong and vigorous (it may be 

 assumed that they were totally or partially 

 polyploid). 4 The leaves have a tendency towards 

 irregularity of shape and color. It is most 

 interesting that species of this group show large 

 differences in duration of this effect of irradia- 

 tion, [increased branching] is particularly evi- 

 dent in the Caryophyllaceae and in the following 

 genera: Impatiens, Clarkia, Antirrhinum, and 



^References given following Chapter 1. 



■•Author's comment. 



104 



