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 miero- 
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) 
Fig. 215.—A Water-Fern Of considerable complexity of struc- 
Seed tecme's 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 r) 
explanation. The pistil is the see 
macrospore-producing leaf or mac- 
rosporophyll, and the stamen is 
the microspore-producing leaf or 
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microsporophyll. Pines and other  Fre.216—TwoIndusiaof Salvinia. 
gymnosperms produce a large cell mi, microspores ; ma, maero- 
(the embryo sac) in the ovule ser? 
(Fig. 217), which corresponds to the macrospore, and a 
pollen grain which represents the microspore. In its 
