INDUCED CHROMOSOMAL ALTERATIONS 1283 



and "clumping" are the most conspicuous effects. Complete "clump- 

 ing" or fusion of nuclear constituents appears to be the ultimate product 

 of a change in chemical composition of chromatin which originates either 

 in general alterations in protoplasmic equilibria or in direct disruption 

 of the nucleoplasm itself. Mature chromosomes share in this "clump- 

 ing" effect which, when less severe, is apparently expressed in a tendency 

 to what has been called "stickiness" and which produces temporary 

 or more permanent unions between chromosomes in mitotic or meiotic 

 stages. 



In appearance, the cytoplasm has usually been described as showing 

 little effect of high-frequency radiation. However, aberrations in 

 formation and functioning of the achromatic figure are frequently 

 reported and the familiar evidence that a certain period usually intervenes 

 between irradiation and the production of visible induced nuclear effects, 

 obviously suggests that the protoplast as a whole is concerned.^ In 

 this connection, a comparative study of the disposition and character 

 of the nonvolatile mineral constituents of the cell (cf. Scott, 38; Good- 

 speed, unpublished) in irradiated and normal tissues after microin- 

 cineration may possibly throw light on the extent and character of 

 induced cytoplasmic vs. nuclear changes. 



Recent investigations of effects of irradiation on nuclear structure 

 deserve more attention because they not only give more definition to 

 types of alteration previously described but in addition emphasize the 

 genetic as well as the cytological significance of what is observed. In 

 particular, it is being shown that the less obvious effects may be of greater 

 genetic and evolutionary importance than the more complete and strik- 

 ing disruptions already known. Clearly, however, the former originate 

 in the same types of disturbances of cellular equilibria as do the more 

 obvious ones; indeed they represent intermediate products of processes 

 culminating in nuclear disruption and lethality (cf. Fig. 1). Thus, 

 fragmentation and fusion, long recognized as major cytological effects 

 of irradiation, become primary agents in genetically significant chromo- 

 somal reorganization, when the processes involved in their production 

 are not carried to their extreme and lethal expression. 



That chromosomal fragmentation is the most frequent and initially 

 important product of irradiation is commented upon by Lewitsky and 

 Araratian (26). In Secale cereale, Vicia saliva, and Crepis capillaris, 

 roots of seedlings X-rayed when one to two days old and fixed two days 

 later showed many mitoses containing chromosomal alterations. In 

 the fragmentation observed, the breakage usually occurred at any point 

 distal to the insertion region. In Crepis it occurred at the insertion 



' The relation between cytoplasmic energization, as expressed in anaphasic stresses, 

 and the appearance of nuclear alterations has elsewhere been discussed (Goodspeed, 

 12). 



