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1903] BEHAVIOR OF THE CHROMOSOMES 275 



growth during the prophase, resulting in an increase in the size 

 of the nucleus and in the quantity of chromatin. 



I The granddaughter chromosomes, having arrived at the poles, 



unite end to end to form a continous daughter spirem in Lilium 

 and in Podophyllum, In all " species examined all identity of 

 the individual chromosomes Is lost in the daughter nucleus. In 



\ Podophyllum and even in Lilium the granddaughter chromo- 



somes show a marked tendency to reticulate, becoming irregular, 

 while in Tradescantia and in the embryo-sac of Lilium the 

 reticulation of the chromatin is continued to such an extent that 

 the daughter nucleus passes almost into the structure of tlie 



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resting stage. 



The chromatin thread or spirem of the daughter nucleus does 

 not undergo a longitudinal fission. During the development of 

 the spindle and in some cases earlier, the daughter spirem seg- 

 ments into the granddaughter chromosomes, which are gradually 

 arranged in pairs in the nuclear plate by means of the spindle 

 fibers. As the granddaughter chromosomes are conveyed to the 

 poles during the anaphase, they are usually in the form of rods, 

 which may be straight, undulating, hooked at one end, or some- 

 times U- or V-shaped. 



The first mitosis in both the micro- and macrospore mother- 

 cells of the higher plants is, therefore, heterotypic, and the second 

 homotypic. These nuclear divisions are not, properly speaking, 

 reducing or reduction divisions. They are not the agents of the 

 reduction, but rather the result of the numerical reduction of the 

 chromosomes. 



In the plants which were the objects of investigation, it is 

 clear that the various forms of chromosomes observed in the 

 heterotypic mitosis are such that might suggest more than one 

 valid interpretation, and it is in a large measure due to this fact 

 that there still prevail different and opposing interpretations in 

 plants as well as in animals. The history of the development of 

 the chromosomes, and a more thorough knowledge of their 

 behavior during every phase of karyokinesis have shown that the 

 shape which the}- may assume is of secondary importance. The 

 form of each chromosome depends chiefly upon the shape of the 



