4 

 CELLS IN DIVISION 



PROPHASE AND TELOPHASE IN THE LIVING NUCLEUS 



In the succeeding pages, observations on the nuclear cycle in a number 

 of living cells in mitosis will be described. The use of living material 

 for such studies has a history of some interest. In 1879 three papers 

 were published on the course of division in the living cells ; Flemming^ 

 and Schleicher^ observed cells of larval Amphibia, and independently 

 published their results in the same volume of one journal; while Stras- 

 BURGER^ described a method of observing the living cells of the staminal 

 hairs of Tradescantia ; and a series of drawings of these cells in division 

 appeared in the following year in a new edition of his ^ellbildung und 

 ^elUheilung.* These studies clearly established that the normal method 

 of nuclear multiplication both in plants and animals consists of a series 

 of complex events in which two new nuclei are formed from one. 

 Flemming's description was the most detailed ; he showed that the later 

 stages of the process are the reverse of the early ones. The decisive effect 

 of these discoveries is well illustrated by a remark of Nordenskiold's^ 

 in comparing the first and third editions of Strasburger's book: 



Even in the first edition (1875), Strasburger makes the nucleus of the egg-cell 

 in the plants he investigated dissolve upon fertilization and its mass disperse into 

 the plasm of the cell; in the latter are then formed a number of concretions, which 

 give rise to fresh nuclei. In the third edition, on the other hand, it is asserted that 

 examples of independent cell formation can no longer be cited from the vegetable 

 kingdom; fresh nuclei invariably arise through the division of older ones. 



In the following decades, studies on living material played a decreas- 

 ing part in the growth of further knowledge of the cell. Advances in 

 microscopical technique, both in methods of staining and in the optics 

 of the instrument were relevant only to the study of fixed preparations. 

 Furthermore, the discovery of Sutton^ that in the reduction division 

 of the germ cells there were events which corresponded to Mendel's 

 segregation and free assortment of the hereditary characters led to 

 researches on cellular anatomy which demanded the utmost resolution 

 of which the microscope was capable; this development necessarily 

 enhanced the tendency of cytologists to work exclusively with stained 

 material. There were still occasional researches on living cells, but they 

 did not directly relate to the dominant concern with the microscopy of 

 inheritance. 



However, interest in the study of the living cell revived, notably in 



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