186 



INTRODUCTION TO CYTOLOGY 



Abnormal temperatures, either high or low, are known to cause 

 aberrations of mitosis in somatic cells and microsporocytes.^ Such effects 

 are responsible for the origin of certain races of plants with altered 

 chromosome numbers, as will be shown in Chapter XX. 



Wounding, such as that occasioned by grafting or decapitation, often 

 disturbs the mitotic process, cells or even branches with altered chromo- 



FiG. 108. — Abnormal mitosis in chloralized root cells of Vicia. A, irregular distribution 

 of chromosomes. B, scattered chromosomes beginning to assume nuclear form. C, 

 nucleus reconstructed by scattered chromosomes. D, chromosomes reconstructing three 

 separate nuclei instead of one. E, chromosomes reconstructing two nuclei connected by a 

 bridge. F, amitosis-like appearance resulting from condition shown in E. {After Saka- 

 mura, 1920.) 



some numbers sometimes resulting.^ Abnormalities also occur in the 

 presence of parasites in gall tissue.^ 



The effects produced by radiations of high frequency^ are of special 

 interest in view of their employment in attempts to analyze the functional 

 differentiations of the chromosomes (Chapters XVIII and XX). Among 

 such radiations the X-rays have been studied most. The cytoplasm of 

 cells treated with these rays may show alterations in viscosity^ and rate of 

 streaming, ^° as well as certain degenerative aspects, such as turbidity and 



^ Borgenstam (1922) on Syringa, Belling (1925a) on Uvularia, Sakamura and Stow 

 (1926) on Gagea, Stow (1926, 1927) and Fukuda (1927) on Solanum, de Mol (1927c, 

 1928a-c?) on Hyacinthus and Tulipa, Rybin (19276) on Nicotiana, Shimotomai (1927) 

 on Scilla, Michaelis (1926, 1928) on Epilohium and (Enothera, Bleier (19306) on 

 Triticum, Koshuchow (1928) on Zea and Cucumis. Bleier (1931c) questions the 

 evidence for the role of temperature in cau.sing natural sterility in Solarium. 



« Winkler (1916) and J0rgensen (1928) on Solanum, Kostoff (1930c, 193 Ice) and 

 Kostoff and Kendall (1931a) on Nicotiana, Lindstrom and Koos (1931) on tomato. 



^ Winge (1927d) on crown gall of Beta; Nemec (1924, 1926) and Kostoff and Kendall 

 (1929a6, 1930a6) on galls of other types. 



^ Certain biological effects of such radiations are reviewed by Packard (1931). 

 Bersa (1926) gives a bibliography. See Popoff (1931) on cell stimulation. 



9 Fairbrother (1928), Wels (1924), Jansson (1927), Nadson (1925). 



»» M. Williams (1923, 1925a), Zuelzer and Philipp (1925). 



