1914] MCALLISTER— EMBRYO SAC OF CONVALLARIACEAE 143 



A normal egg apparatus is formed from the 3 micropylar nuclei. 

 In other respects as well the embryo sac seems normal. 



Polygonatum commutatum 



In Polygonatum commutatum the megaspore mother cell is 

 frequently hypodermal (fig. 45), or it may be separated from the 

 epidermis by one or two layers of cells (fig. 46). The mother cell 

 divides twice to form an axial row of 4 permanently separated 

 megaspores (figs. 47, 48). The inner spore enlarges by vacuoliza- 

 tion, while the outer 3 gradually shrivel and disorganize (fig. 49). 

 Three divisions of the nucleus of this functional megaspore form the 

 8 nuclei of the mature embryo sac (figs. 50, 51, 52). A normal 

 embryo sac is organized from the 8 nuclei thus formed. The 2 

 polar nuclei fuse early, and the fusion nucleus lies in close proximity 

 to the antipodal cells until immediately before fertilization, when it 

 takes up a position near the egg. 



This mode of embryo sac development has been called the 

 normal' ' as contrasted with the "lily type" of development. It 

 seems clear, especially from the embryo sac behavior in the Con- 

 vallariaceae, that no one type of development can be regarded as 

 normal.' ' 



I have show r n that in the cases of Smilacina stellata and S. 

 icemosa (18. 10) reduction in the number of the chromosomes takes 





. . 



mesasDore mo 



While I have been unable to make reliable countings of the chromo- 

 somes in the case of the other species studied, I have found evidences 

 of the reduction divisions, such as the synapsis stage and double 

 heterotypic chromosomes, in all the forms investigated, with the 



Strcptop 



mother cell. In view 



mentioned above, it seems 



Smilacina stellata and S. racemosa, reduction in the chromosome 

 number accompanies the first two divisions of the mother cell in the 



of the group which I have studied- In Clintonia (23), 



members 



evidence 



divisions. 



megaspore 



