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1903] BEHAVIOR OF THE CHROMOSOMES 273 



serves to show more definitely the close resemblance between 

 embryo-sac and pollen mother-cell (Mottier, '98, _/?^. j/). 



Juel (^igoo) has shown that the two successive divisions in 

 the macrospore mother-cell of Larix gives rise to four cells in 

 the same manner as in such angiosperms as Helleborus, and that 

 the first of these mitoses is heterotypic. This is probably true 

 for many other gymnosperms. 



It is well known that the developmental history of the 



embryo-sac between the macrospore mother-cell and the mature 



female gametophyte is shortened in certain cases by one or two 



^ nuclear divisions, and it is important to know, in these cases of 



abbreviated development, the place occupied by the two mitoses 

 in question. 



With this object in view Frau Schniewind-Thies (1900) has 

 investigated the development of the embryo-sac in several 

 species of the Liliaceae, and has brought together a number of 

 interesting observations. In all cases examined by this author, 

 the first two nuclear divisions in the mother-cell are heterotypic 

 and homotypic respectively, and whenever four potential spores 

 result, each nuclear division is followed by a cell-division. One 

 of these potential macrospores, usually the lower one, develops, 

 as in Helleborus, by three successive typical or ordinary mitoses 

 into the embrvo-sac* In the case of Scilla sibirica, however, the 

 developmental history of the female gametophyte, or embryo- 

 sac, is shortened by only one nuclear division. The first or 

 heterotypic division is followed by a cell-division. Following 

 the second, or homotypic mitosis, no cell-division takes place, 

 and consequently each daughter cell contains two nuclei. Either 

 of these cells may function as the' macrospore, and develop 

 into the embryo-sac, while the other is absorbed. In this case 



e homotypic division represents the first mitosis in the spore. 

 The two daughter nuclei now divide twice in the typical way to 

 give rise to the mature embryo-sac. In Scilla sibirica, therefore, 



ere is a shortening of the development by one typical mitosis. 



In Lilium and in other.genera with a similar development of 



the embryo-sac, the process is further shortened. Here the 



macrospore mother-cell functions at once as the spore. No cell 



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