302 



FOUNDATIONS OF BOTANY 



non-sexual generation, the sporophyte, often being of large 



size. The ferns (non-sexual generation), for instance, are 

 perennial plants, some of them tree- 

 like. 



Some pteridophytes, as the Salvinia, 

 a small floating aquatic plant, some- 

 times known as a water-fern (Fig. 

 215), produce two kinds of spores, 

 the large ones known as macrospores, 

 and the small ones known as micro- 

 spores (Fig. 216). Both kinds pro- 

 duce microscopic prothallia, those of 

 the former bearing only archegonia, 

 those of the latter only antheridia. 

 From the prothallia of the macro- 

 spores a plant (non-sexual generation) 

 of considerable complexity of struc- 

 ture is formed. 

 374. Parts of the Flower which correspond to Spores. 



In seed-plants the spore-formation of cryptogams is repre- 

 sented, though in a way not 



at all evident without careful 



explanation. The pistil is the 



macrospore-producing leaf or mac- 



rosporophyll, and the stamen is 



the microspore-producing leaf or 



microsporopTiyll. Pines and other 



gymnospenns produce a large cell 



(the embryo sac) in the ovule 



(Fig. 217), which corresponds to the macrospore, and a 



pollen grain which represents the microspore. In its 



FIG. 215. A Water-Fern 

 (Salvinia). 



ma 



FIG. 216. Twolndusiaof Salvinia. 



mi, microspores ; ma, macro- 

 spores. 



