CHAPTER VI 



in the same, sometimes in different plants. After the sperm cell 

 swims down the archegonium and unites with the egg cell, there 

 grows from the fertilized cell, a spore-bearing body ; in the liverwort, 

 No. 9 in the illustration, this body is like a little umbrella ; it is 

 sometimes urn-shaped, sometimes a mere sphere beneath the frond. 

 This spore-bearing body remains attached to the mother plant, and is 

 mainly supported by it, though it may assist in food-making. The 

 moss spore produces first a branching, filamentous body resembling 

 some of the green algae, but soon, from buds on these filaments num- 

 bers of tiny plants arise, each consisting of stem, root-hairs and leaves, 

 that is, the part of the plant that is commonly noticed. The antheri- 

 dia and archegonia are produced among these leaves, sometimes in 

 the midst of leaf rosettes which resemble flowers. After an egg cell 

 in an archegonium has been fertilized, the spore-bearing body begins 

 to grow ; it is usually urn-shaped and borne on a stalk. As in the 

 liverworts, this spore-bearing part remains attached to the sexual 

 plant, but it has always green cells and stomata and helps in food- 

 making. 



From the fern spore grows the prothallium, which, in all our 

 species, much resembles the first generation of the liverwort. The 

 prothallium bears archegouia and antheridia, and from an egg cell, 

 after the sperm cell is united with it, grows the plant we commonly 

 call the fern. This spore-bearing plant becomes capable of nourish- 

 ing itself very early in its existence, and the sexual plant perishes. 

 So the first generation of the fern is comparatively minute, and has a 

 brief existence ; the second generation is of considerable size, it is 

 as well equipped as flowering plants for supporting itself, and it may 

 live for years. The first generation of the horsetail, Equisetum, is 

 even smaller than the fern prothallium, while, as we have seen, the 

 sporophyte is a complex plant of long duration. 



Perhaps the most interesting Pteridophyte, biologically, is a small 

 club-moss, Selaginella. One species is common on California foot- 

 hills and mountains. It might be mistaken for a very hardy moss ; 

 its stems are woody and much branched and its closely crowded leaves 

 are as small as moss leaves but much thicker. The Selaginella pro- 

 duces, in the axils of leaves, two kinds of spores, macrospores and 

 microspores, that is, large spores and small spores. Four of the large 

 spores fill a macrospore case, while a microspore case contains many 

 spores. Both kinds of spores fall to the ground and germinate. The 

 prothallium growing from the macrospore always produces arche- 

 gonia containing egg cells, but the prothallium is minute and merely 

 protrudes from the thick spore wall, which also encloses a store of 



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