appear. After 5. 5 hours there are still fewer 

 normal figures. The action of X rays on Vicia 

 faba manifests itself in the loss by young cells 

 of [their] embryological character and in their 

 exhibiting signs of senescence. Transformation 

 into permanent [mature] tissues proceeds from 

 the zone of elongation and, eventually, includes 

 part of the root tip. The undulation and wrin- 

 kling of the root surface are related to the 

 transformation of periblem tissues into perma- 

 nent ones. Premature transformation of the 

 embryological cells into permanent components 

 is indicated by enlargement of the nucleus. The 

 variety of anomalies due to the primary effects 

 are based on the fact that nuclei, at the time of 

 exposure, are found in various stages of 

 division. 



The secondary effects show up in nuclei 

 which began mitosis in an injured condition. 

 The migration of chromosomes is irregular, 

 not only in timing, but also in location. The 

 unequal migration of chromosomes gives rise 

 to micronuclei. Furthermore, binuclear and 

 polynuclear cells arise as a result of the failure 

 of new cell walls to form. Chromosomes often 

 carry additional spindle fibers and are clearly 

 visible. Nuclei in the resting stage show pre- 

 mature senescence as revealed by the forma- 

 tion of chromocenters. At the same time vari- 

 ous degenerative forms are encountered (kary- 

 orhexis, pycnosis, karyolysis), whose number 

 increases with the time interval after irradiation. 



Tschassownikow (1928) considers that it is 

 characteristic for basophilic elements to domi- 

 nate the acidophilic ones in cell nuclei of normal 

 liver cells. From 9 to 12 hours after irradia- 

 tion the nuclei show the first changes which, in 

 general, lead to the accumulation of basichro- 

 matin. The accumulation of basophilic granules 

 and lumps near the nuclear membrane is the 

 first indication of degeneration of the nucleus. 

 This phenomenon is known as hypermitosis of 

 the nuclear membrance. As a result of these 

 processes the number of basophilic particles 

 increases and, at the same time, the basophilic 

 substance begins to penetrate the nuclei by 

 diffusion. These phenomena characterize the 

 onset of pycnotic changes which lead to total 

 degeneration. Blakeslee, Bergner, Satina, 

 Avery, Cartledge, and Potter, in 1929, ex- 

 amined plants which had been grown from 

 two groups of X -irradiated seeds of Datura 

 stramonium, one group exposed for 50 min- 

 utes; the other for 65. Of the nine plants in 

 the first group only one was normal; of the 

 seven plants in the second group none was nor- 

 mal. Various types of chromosome config- 

 urations were observed in these plants, usually 

 involving 4 or 6 chromosomes. There were 

 two cases of simple translocation (chain), 5 to 

 7 cases of segmental interchange or reciprocal 

 translocation (ring), and one case of fragmental 

 adhesion. Fourteen of these plants had poor 

 pollen. 



Sapegin (1930) pointed out that after 480 

 plants of several pure winter and spring wheat 

 strains were irradiated, hundreds of changed 

 descendants arose, the majority of which were 

 chromosomal aberrants. The aberrations of 

 the chromosomes were various: univalent, 

 fragments, asynaptic, chromosomal adhesions 

 [translocations?] and trivalent and quadrivalent 

 formations. 



Delone (1930) subjected young ears of 

 Triticum vulgare albidum and T. durum melan- 

 opus to irradiation. Experiments were subse- 

 quently conducted only with the first of these 

 plants. These experiments revealed, first of 

 all, that the later the plants were irradiated, 

 the greater was the degree of infertility of the 

 ears (Table 25). 



The seeds gathered from the irradiated 

 ears gave rise to numerous mutations (see 

 Chapter 2) containing various chromosomal 

 aberrants. 



Mutation 2N - 1 -h i3. This mutation was 

 represented in Xi by one small plant with a 

 single ear. Cytological analysis revealed that 

 this plant had in its cells only 41 chromosomes 

 and that in place of the missing chromosome it 

 had a tiny fragment. This was probably a frag- 

 ment of the 42nd chromosome. It divided evenly 

 and was not lost in karyokinesis. The ear of 

 this plant gave four well developed seeds which 

 yielded four plants differing both from the 

 parent plants and from the Xi plant. The frag- 

 ment in the nuclear plate was not lost, but it 

 was greatly enlarged. Nevertheless, this |3 

 fragment was approximately one -fifth the length 

 of an average chromosome of wheat. In another 

 mutation two chromosomes in Xi were shorter 

 than normal ones. A third mutation (complex 

 polysomic) had in its chromosome set 45 units 

 (three more than normal). It had 43 long 

 chromosomes, one short fragment, and one 

 round a. The formula for the karyotype of this 

 plant can be written as follows: 2N -I- 1 -I- 1/2 

 + a. This is a complex instance of polysomy 

 and chromosomal fragmentation. A fourth mu- 

 tation is a simple monosomic one with a karyo- 

 type formula of 2N -I- 1. 



Plotnikowa (1931) also used soft wheat 

 (Triticum vulgare var. ferrugineum ) for her 

 investigations. Ears which had been cut off 

 the plant at the time that they were undergoing 

 reduction-division were exposed to radiation. 

 At diakinesis or metaphase of the irradiated 

 cells it is rarely possible to count 21 chromo- 

 somes; usually the chromatin material fuses 

 into a ball. A small part of the chromatin 

 material distributes itself throughout the plasma 

 in the form of small drops. At early anaphase 

 the chromatin stretches out in the direction of 

 the spindle fibers, forming threads, which are 



67 



