OTHER FERN-LIKE PLANTS: CLUB MOSSES 



379 



spores, which means large spores. The upper spore cases produce 

 a very large number of small spores (micros pores) . Since the spores 

 are of different sizes, Selaginella is said to be a heterospoms plant. 

 A plant is homosporus when the spores are all alike. 



533. The prothallia or gamete plants (gametophytes) of 

 Selaginella. The gamete plants of Selaginella are diceceous (or 

 heterothallic] . This condition of the prothallium is deter- 

 mined in the spore. The small spores (microsppres) pro- 

 duce small male gamete plants. There is only one cell 

 in the prothallium part. The other cell, which is larger, 

 develops into the sperm case with a wall containing a 

 few sperms. The sperms are biciliate, as they are in the 

 lycopods, thus being different from those of the ferns and 

 horsetails, and more like those of the mosses. The large 



Fig. 350. 



Section of mature macro- 

 spore of Selaginella, showing 

 female prothallium and arche- 

 gonia. (After Pfeffer.) 



Fig. 351- Fig. 352. 



Mature female prothallium of Seediinz of Selagi- 



Selaginella just bursting open nella still attached 



the wall of macrospore, expos- to the macrospore. 



ing archegonia. (After Pfeffer.) (After Campbell.) 



spore (macrospore or megaspore) develops the female gamete 

 plant. This never escapes from the spore wall. A mass of 

 tissue is formed which cracks open the spore wall, and the egg 

 cases (archegonia) are developed in the exposed surface. There 

 is no chlorophyll in either male or female prothallia. This 

 accounts for their small size, the larger female prothallium being 

 due to the greater amount of food in the large spore. All the 

 food, therefore, for the gamete plant of Selaginella, comes from 

 the spore plant (sporophyte) and was stored in the spores while 



