﻿1903] BEHAVIOR OF THE CHROMOSOMES 271 



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seems furthermore exceedingly probable that the longer and 

 more uniform turns of the spirem will t furnish the regular and 

 straight chromosomes, whilst the less regular parts — for such 

 exist in the majority of the daughter nuclei in question — give 

 rise to the short, kinked, or knotted ones. 



It may be mentioned In passing that every step in the devel- 

 opment of the spindle seems to bear direct evidence in favor of 

 the view that the arrani^^ement of the chromosomes is accom- 

 plished by a pushing and pulling action of the spindle fibers. 



Relative to the behavior of the chromatin, it may be stated 

 finally that the possibility is not excluded that in some cases the 

 pirem may be formed double, in part or entirely, but direct 

 evidence of such a possibility was not observed save in the 

 presence of two rows of chromatin granules in portions of the 

 thread-work of the daughter nucleus. 



The daughter nucleus in the lower end of the embryo-sac, 

 which gives rise ultimately to the antipodal cells and the lower 

 polar nucleus, behaves in division exactly as the upper, and the 

 fact that this nucleus presents a larger number of chromosomes 

 only adds more difficulties to the problem of the chromosomes. 



In certain respects, the third karyokinesis In the embryo-sac 

 of Lilhun Martagon resembles the second. This is true as regards 

 the development of the spindle whose fibers penetrate the nuclear 

 cavity before the chromatin spirem is entirely segmented into 

 the chromosomes (see Mottier, 'g^i, figs. 16, ly). The behavior 

 of the chromatin, however, is quite like that in ordinary and 

 typical vegetative cells. 



The first' two mitoses in the spore mother-cells of higher 

 plants, therefore, are heterotypic and homotypic respectively, 

 these terms being used in the sense of Flemming. The chief 

 distinguishing characteristic of the heterotypic nuclear division 

 is the double longitudinal fission of the chromosomes. The 

 shape of the chromosomes is without importance, since the form 

 of the individual chromatin elements, which often varies in the 

 same nucleus, is due to different causes. This division is further 

 characterized in plants by a rather long period of growth during 

 the prophase which results in a marked increase in the size of 



