18G 



ELEMENTS t . !' STRUCTURAL IJOTANV. 



of tissue in which arc developed cells corresponding to th" 

 pollen-grains of phanerogams. These projections are the 

 antheridia; they contain cells in which are fertilizing bodies 

 known as antherozoids. Also on the under surface of the 



prothallium, near the notch, 

 we find structures analogous 

 to the embryo-sac of the 

 phanerogamous ovule. These 

 are the archegonia. They 

 are mostly flask-shaped bod- 

 ies, having a germ-cell the 

 oosphere in the lower cud. 

 The antherozoids, on escap- 

 ing from the antheridia, 

 make their way down the 

 necks of the archegonia, and 

 coming in contact with the 

 oospheres fertilize them. As a result of this fertilization, 

 a plant is developed in all respects like the one which 

 originally bore the spores on its fronds. 



326. It is manifest, then, that we have here two distinct 

 generations : first, the spore produces the prothallium 

 which bears the antheridia and archegonia ; secondly, the 

 interaction of these gives rise to a plant which bears the 

 spores. This phenomenon is spoken of as the alter nati<i 

 of generations. 



327. The stems and roots of Ferns are found to contain 

 vascular bundles which, like those of monocotyledons, arc 

 closed. 



Fig. 235. 



Fig. 235. Prothallium of a Fern, under side ; h, root-hairs; an, autheridlv 

 ar, archegonia. Magnified 10 times. (Prantl.) 



