180 PLANT STEUCTUKES 



ovule develops, did not escape early attention, and it was 

 called endosperm, meaning "within the seed." The endo- 

 sperm of Gymnosperms, therefore, is the female gameto- 

 phyte. 



At the margin of the endosperm nearest the micropyle 

 regular flask-shaped archegonia are developed (Fig. 149, a), 

 making it sure that the endosperm is a female gameto- 

 phyte. It is evident that the necks of these archegonia 

 (Fig. 149, c) are shut away from the approach of sperms by 

 swimming, and that some new method of approach must be 

 developed. 



100. Male gametophyte. — The microspores are developed 

 in the sporangium in the usual tetrad fashion, and are pro- 

 duced and scattered in very great abundance. It will be 

 remembered that the male gametophyte developed by the 

 microspore of Selaginella is contained entirely within the 

 spore, and consists of a single ordinary prothallial cell 

 and one antheridium (see § 89). In the pine it is no bet- 

 ter developed. One or two small cells appear, which may 

 be regarded as representing prothallial cells, while the rest 

 of the gametophyte seems to be a single antheridium (Fig. 

 146, D). At first this antheridium seems to consist of a 

 large cell called the wall cell, and a small one called the 

 generative cell. Sooner or later the generative cell divides 

 and forms two small cells, one of which divides again and 

 forms two cells called male cells, which seem to represent 

 the sperm mother cells of lower plants. The three active 

 cells of the completed antheridium, therefore, are the wall 

 cell, with a prominent nucleus, and two small male cells 

 which are free in the large wall cell. 



These sperm mother cells (male cells) do not form 

 sperms within them, as there is no water connection be- 

 tween them and the archegonia, and a new method of 

 transfer is provided. This is done by the wall cell, which 

 develops a tube, known as the pollen-tube. Into this tube 

 the male cells enter, and as it penetrates among the cells 



