CELL DIVISION, MORPHOLOGY, VIABILITY 



815 



binucleate cells observed by Takamine (1923) in Allium root tips 1 hour 

 after treatment with 2500 A radiation. 



Normally, in the grasshopper neuroblast, the cleavage furrow forms 

 near one end of the elongated anaphase cell and the resulting daughter 

 cells are unequal in size; the daughter neuroblast is large, while the 



Q 



Fig. 11-17. Diagram showing ultraviolet-induced abnormalities in mitosis of the 

 Chortophaga neuroblast. A-G, treatment at late metaphase or early anaphase; 

 spindle abnormally short (A), cleavage furrow appears at cell equator (B, C) to give 

 an equal division (D, E) or a secondarily produced unequal division (F, G). H-L, 

 treatment at prometaphase or early metaphase with a dose sufficiently large to prevent 

 centromere division and chromosome separation. Spindle greatly reduced, its sub- 

 stance mainly in the form of a hyaline globule (hg); note pseudopodia and distal 

 separation of chromatids (I-K) {from Carlson and Hollaender, 1948). 



daughter ganglion cell is small. The reduction in spindle size induced by 

 2250 A radiation is apparently correlated with a tendency of the cleavage 

 furrow to form at the cell equator (Fig. 11-17) (Carlson and Hollaender, 

 1948). In many cells, as the cleavage furrow deepens, the bulk of the 

 cytoplasm flows toward one of the poles, so that two more or less normal 

 daughter cells of unequal size are formed. In some cells, however, no 



