LIFE HISTORY OF PINUS 



79 



make " an individual by coalescence," that is, they are physi- 

 ologically one. 



This is not the place to enter into a detailed discussion of the 

 homologies of the embryo-sac, but I believe that the suggestion 

 herein made will form an interesting working basis, and it may 

 bring us nearer to a true conception of these structures than we 

 have yet attained. But whatever our opinion regarding the ele- 

 ments within the embryo-sac, it is clear that we cannot longer 

 use the terms macrospore and embryo-sac interchangeably as so 

 many writers have done. We now know that a tetrad division 

 may occur within the ovule and it has been shown that the 

 embryo-sac may result from the germination of a single macro- 

 spore, that it may be formed directly from the macrospore- 

 mother-cell, or that it may have its origin in one of the daughter- 

 cells formed as the result of the heterotypical division. In any 

 case would it not be far less confusing if we should designate 

 the multicellular bodies, developed within the macrosporangium 

 and the microsporangium of the higher plants, as embryo-sac 

 and pollen-grain, or female and male gametophyte, respectively, 

 and should retain the terms macrospore and microspore for the 

 true spores in their one-celled stage? 



LATER HISTORY OF THE AXIAL ROW. 



The Fate of the Upper Cells. Whether the number of cells 

 in the axial row of Pinus be three or four the female gameto- 

 phyte is always the product of the lowest cell. Very shortly 

 after the second division is completed, the upper cells of the 

 axial row give evidence of disintegration, while the basal cell 

 increases much in size, its nucleus becoming very large. The 

 nuclei of the four spores in Larix are very similar, Juel ('oo), 

 fig. 18, but in Pinus the basal cell is markedly different from 

 the others at a very early date (figs. 144, 145, plate XIV). The 

 upper cells of the axial row gradually disintegrate, and are 

 crowded to one side by the growth of the macrospore, remain- 

 ing for a time as deeply staining, amorphous masses which 

 finally disappear altogether (figs. 69, plate VI and 147, 148, 

 plate XIV). Instances in which one of the upper cells of the 

 axial row in Angiosperms becomes the functional macrospore 



