640 LECTURE XXIII. 



vesicle contains a portion of the nucleus of the mother-cell 

 which is excluded from taking part in the formation of the 

 antherozoid. Probably in all cases a portion of the nuclear 

 substance of the mother-cell is thus excluded. The excluded 

 portion of the mother-cell is termed a polar body. 



In order to complete our study of the peculiarities at- 

 tending the development of male reproductive cells, we must 

 enquire whether any indication of the formation of a polar 

 body can be detected in connexion with the processes already 

 mentioned (p. 615) as going on in the germinating pollen- 

 grains of Phanerogams. In all cases the nucleus and the pro- 

 toplasm of the pollen-grain, in the first instance, undergo 

 division, so that two cells are formed which Strasburger dis- 

 tinguishes respectively as the vegetative and the generative. 

 Of these, the former is much the smaller in the Gymnosperms, 

 whereas the converse is the case in the Angiosperms. In the 

 Gymnosperms the two cells are permanently separated by a 

 cell-wall, but in the Angiosperms the cell-wall sooner or later 

 undergoes absorption, so that the only permanent evidence of 

 the cell-division is the presence of the two nuclei. In some 

 Gymnosperms two or three more vegetative cells may be 

 successively cut off from the generative cell. The vegetative 

 cell is usually considered to represent the rudiment of the 

 vegetative portion of the male prothallium, but Strasburger 

 attaches to it the physiological significance of a polar body. 

 In view of the fact that in the majority of observed cases the 

 whole of the generative nucleus takes part in the sexual 

 process, no portion of it being excluded, it seems probable 

 that Strasburger is right in regarding the vegetative cell as 

 being physiologically a polar body. 



Strasburger extends his view to the vegetative cell which is formed in 

 the germinating microspore of the Heterosporous Vascular Cryptogams. 

 In this we are unable to follow him, since, as mentioned above, a polar 

 body is formed in each mother-cell of an antherozoid in these plants. 

 The vegetative cell in this case is simply of morphological, and not of 

 physiological, significance. 



Turning now to the development of well-differentiated 

 female gametes, we find many more or less well-marked cases 



