546 



LIFE-HISTORIES 



Fig. 375. — Selaginellas. Germination of microspores. A-E, difTerent views 

 of the spore showing the prothallus-cell (p), cells of the antheridium- 

 wall (w), and the cell producing spermatozoids (s), ^^. In E the cell- 

 walls have dissolved previous to discharging the spermatozoids. F, 

 spermatozoids, ^f-"-. (Belajeff.) 



The spores begin to germinate while still within the sporangium. 

 The contents of each microspore divides into several cells (Fig. 375, 

 A-D) one of which (p) represents the vegetative part of a male 

 gametophyte, the others constituting a male gametangium, in the 

 center of which is formed a cluster of elongated gametes closely 

 resembling the male gametes of a liverwort. After leaving the 

 sporangium the microspores liberate their motile gametes by rup- 

 ture of the wall. The large cell which constitutes the macrospore 

 is rich in reserve food and begins to germinate by dividing into a 

 number of small cells within the wall. Soon the macrospores are 

 set free from the sporangium, and continue to germinate by forming 

 a few archegonia on the upper side, which eventually i)rotrudes from 

 the ruptured spore-wall shown in Fig. 376. After fertilization, the 

 egg-cell divides into an upper and a lower half, the lower half grow- 

 ing into an embryo, while the upper half develops into a peculiar 

 organ called the suspensor (et). This by its elongation pushes the 

 embryo, foot foremost, into the mass of vegetative cells upon which 

 it feeds. The root and the shoot of the young embryo (Fig. 377) 

 finally protrude from the macrospore, the foot (/) still remaining 

 within as an organ of absorption in contact with the food supply. 

 There are two cotyledons, which, containing chlorophyll, soon begin 

 to make food for the plantlet, and aided by the developing leaves of 

 the plumule, finally render the .young plant self-supporting. From 

 the upper side of each cotjdedon (and often on later leaves) a flat 



