﻿THE BEHAVIOR OF THE CHROMOSOMES IN THE 



SPORE MOTHER-CELLS OF HIGHER PLANTS 

 AND THE HOMOLOGY OF THE POLLEN AND 

 EMBRYO-SAC MOTHER-CELLS. 



David M. Mottier. 



) 



There is probably no other problem which has presented 

 greater difficulties to the botanical cytologist than the behavior 

 of the chromosomes during the two successive nuclear divi- 

 sions in the spore mother-cells of the higher plants. This is at 

 once apparent, even to those who are not specialists in this 

 field, from the different interpretations which have been 

 advanced from time to time, and from the various and contra- 

 dictory doctrines that are still held by different investigators. 



From the zoological side, we are indebted to Flemming and 

 his students for the first correct interpretation of the behavior 

 of the chromosomes in the two successive nuclear divisions m 

 the spermatocyte of Salamandra. 



Flemming designated the first of these divisions as ** hetero- 

 typic *' and the second as "homotypic." The first division in 

 Salamandra is characterized by a long period of growth of the 

 cell and nucleus during the prophase, the appearance of the 

 reduced number of chromosomes and their double longitudinal 

 splitting; the first longitudinal fission taking place during the 

 prophase and the second during the metaphase or anaphase. 



The striking parallel between the first two mitoses in the 

 micro- and macrospore mother-cells of higher plants and those 

 of the spermatocyte of Salamandra has frequently been pointed 

 out, and the terms heterotypic and homotypic have been app 

 priately applied to them. 



Recent investigations have shown that in the spore mother- 

 cells of certain higher plants the first mitosis is especially 

 characterized also by a long period of growth during the pro- 



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