142 



ELEMENTARY STUDIES IN BOTANY 



by nuclei or naked cells). It would be hard to imagine a 

 gametophyte reduced to lower terms, and it is not at all 

 surprising that the pollen grain was thought to be the male 

 cell, rather than a spore containing a male gametophyte. In 

 fact, no one would have recognized these three cells or nuclei 



as a gametophyte, if 

 the gametophytes of the 

 Gymnosperms and the 

 Pteridophytes had not 

 been studied. 



The female gameto- 

 phyte (within the mega- 

 spore that is in the 

 nucellus) at first consists 

 usually of eight nuclei, 

 which become arranged 

 very definitely (Fig. 114). 

 When the megaspore ger- 

 minates to form the ga- 

 metophyte, it ceases to 

 be a, spore, and is repre- 

 sented only by the encas- 

 ing wall that surrounds 

 the gametophyte. The 

 cavity thus inclosed is 

 called the embryo-sac. 

 In other words, we speak 

 of the megaspore until 



it begins to germinate, and then we call the same cavity 

 an embryo-sac. This name was given before there was 

 any knowledge of the existence of a megaspore or a 

 female gametophyte within an ovule, for it was .seen that 

 the embryo appeared in a sac-like cavity. Within this 

 embryo-sac three of the eight nuclei become placed in the 

 end of the sac towards the micropyle, and are organized into 



FIG. 114. The female gametophyte of a lily, 

 having developed within the megaspore, 

 which is within the nucellus of the ovule ; in 

 the end of the embryo-sac (the name given 

 to the megaspore when the gametophyte 

 begins to develop) towards the micropyle 

 (m) is a group of three cells, one of which is 

 the egg (e) ; at the other end of the sac is 

 another group of three cells ; in the midst of 

 the sac the two nuclei are seen which are to 

 fuse and form the endosperm nucleus. 



