DIV. I 



PTERIDOPHYTA 



525 



lateral branches, while from the under side spring the dichotomously-branched 

 roots (Fig. 491). The cone -like flowers, consisting of the closely-aggregated 

 sporophylls, are situated in groups of two or more at the ends of the forked 

 erect shoots. The sporophylls are not like the- sterile leaves in shape ; 

 they are broader and more prolonged at the tip ; each bears a large reniform 

 sporangium on the upper side at the base. The sporangium opens into two 



FIG. 492. ,4, Germinating spore of Lycopodium annotinum; r, rhizoid cell; &, basal cell; s, 

 apical cell ; sp, spore-membrane (x 580). B, Older stage of the prothallus of the same species, 

 showing the endophytic fungus (p) in the lower cells, and the apical cell divided into three 

 meristematic cells (x 470). C, Lycopodium. complanatum. Prothallus with antheridia (an), 

 archegonia (ar), and a young embryo (fc) ( x 26). (After BRUCHMANN.) 



valves and sets free numerous minute spores (Fig. 491 H). Lycopodium 

 Selago differs in habit from the other species ; its bifurcately-branched stems 

 are all erect, and the fertile are not distinct from the vegetative regions of the 

 shoots. 



The spores of the Lycopodiums are all of one kind, and in consequence of their 

 formation in tetrads are of a tetrahedral though somewhat rounded shape. The 

 exospore is covered with a reticulate thickening (Fig. 491 J, K). 



The prothallia developed from the spores show a remarkable variety in the 



