PTERIDOPHYTA. 227 



and in L. inundatum, it is a small tubercular body which has a subterranean 

 portion, with either little or no chlorophyll; and an aerial green portion. 

 The prothallia of L. phlegmaria and others live saprophytically in the crevices 

 of the bark of trees ; they are partly filamentous, branched, and possess no 

 chlorophyll. 



The asexual generation. PERENNIAL PLANTS. The stem 

 branches monopodially (often apparently dichotomously), and is , 

 thickly covered by small, simple, triangular or scale-like leaves. 

 The leaves are spirally arranged in some species (Figs. 229, 230), 

 and in others, whose stem is compressed with unequal sides, oppo- 

 site (Fig. 231). The roots of Lycopodium are dichotomously 

 branched. 



The SPORANGIA in Lycopodium are situated singly at the base of 

 the leaves, almost in their axils j they are reniform, unilocular and 



FIG. 232. Lycopodium clavatum. A 

 tetrahedral spore seen from above, 

 FIG. 231. Lycopodium complttnatum : a where the three borders join ; and a 



leaves on the edges of the stem ; d leaves on tetrad of bilateral spores, still lying 



the sides. in the mother-cell. 



open like a mussel-shell by two valves (Fig. 230 fc). The sporangia 

 are developed from a group of surface cells. The archesporium is 

 formed from one hypodermal cell (or perhaps a cell -row). 



The fertile leaves are collected upon definite regions of the stem. 

 They are either similar to the barren ones, and then the fertile 

 portions of the stem pass gradually, without any break, into the 

 barren portion (L. selago) ; or they differ from the barren leaves, 

 and are then collected into special apical cones (Fig. 230 a). The 

 SPORES are tetrahedral or bilateral (Fig. 232). 



About 100 species, chiefly tropical. 



Five species of Lycopodium are found in Great Britain. L. clavatum and L. 

 selago are common in mountainous districts. L. annotinum is common in the 



