460 



BOTANY 



PART II 



covered with small, awl-shaped leaves, creeps along the ground ; it branches 

 dichotomously, and gives rise to ascending lateral branches, while from the under 

 side spring the dichotomously branched roots (Fig. 422). The cone-like flowers, con- 

 sisting 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 valves by a transverse slit, 

 and lets free numerous minute spores 

 (Fig. 422 H). Lycopodium Sclago differs 

 kj in habit from the other species ; its 

 G> bifurcately branched stems are all erect, 

 and the flower-cones are not distinct 

 from the vegetative region of the fertile 

 shoots. 



The spores of the Lycopodiums are 

 all of one kind, and in consequence of 

 their formation in tetrads are of a tetra- 

 hedral though somewhat rounded shape. 

 The exine is covered with a reticulate 

 thickening (Fig. 422 J, K). 



The mode of germination and de- 

 velopment of the sexual generation 

 have as yet been determined only for 

 a few species. The prothallia of Lyco- 

 podium clavatum and the closelyrelated 

 L. annotinum are small white tuberous 

 .structures, which live as subterranean 

 saprophytes. At first top-shaped, they 

 become converted by the continued 

 marginal growth into cup-shaped lobed 

 bodies, which may attain a size of two 

 centimetres. Long rhizoids spring 

 from the lower surface, while the upper 

 surface bears numerous antheridia and 

 archegonia. In L. complanatum (Fig. 

 423) the subterranean prothalli are 

 turnip-shaped, in L. Selago rounded or 

 elongated and cylindrical. The pro- 

 thalli of the latter may be developed 

 on the surface of the soil, in which case they are green. In the case of L, 

 inundatum, the prothalli of which are found on damp peaty soil, and in the 

 tropical L. cernuum t with erect profusely branched shoots, the prothallia are poor 

 in chlorophyll and are attached to the soil by rhizoids ; they have the form of 

 small, half-buried, cushion-like masses of tissue, which give rise to green aerial 

 thalloid lobes. The archegonia occur at the base of these lobes, the antheridia 

 also on their surface. 



The prothallia are all monoecious. The antheridia are somewhat sunk in the 

 tissue (Fig. 422 C) and enclose numerous spermatozoid mother- cells, in which 

 small biciliate spermatozoids are formed. The archegonia (Fig. 422 E, F) are 



Fi<;. 423. Lycoixxlium r////>/i''^/H. Prothallus 

 with antheridia (), archej^onia (or), and a young 

 embryo (k). (After BRUCHMANN. x 26.) 



