SECT. I 



CRYPTOGAMS 463 



sporangial wall, the tapetal layer, is not absorbed. The sporangia have 

 no annulus. Except in the case of hades, the spores of which become 

 free by the decay of the sporangial wall, they dehisce by longitudinal 

 slits, which divide the sporangia into two valves ; the slits occur 

 where rows of cells of the wall have remained thin i^^''''). The sporangia 

 of Lijcopodium are homosporous ; those of Selaginella and Isoetes are 

 heterosporous. The heterosporous forms produce only greatly modified 

 and reduced prothallia ; in the genus Lijcopodium, on the other hand, 

 the prothallia are well developed, and show certain resemblances to 

 those of the Ophioglossaceae. 



The Lycopodiaceae and the Selaginellaceae agree in the segmentation of the 

 embryo, which in both is characterised by possessing a suspensor, and in the 

 structure of the spermatozoids, which are bi-ciliate. The Isoetaceae on the otlier 

 liand have multiciliate spermatozoids and the embryo has no suspensor. On these 

 grounds the two sub-classes of Lycopodiaceae biciliatac and Lycopodiaceae pluri- 

 ciliatac may be distinguished. 



Order 1. Lyeopodlaeeae (^^") 



Tlie numerous, widely distributed species of the genus Lycopudium (Club Moss) 

 are for the most part terrestrial plants ; in the tropics many epiphytic forms also 

 occur. In LTjcopodium clavatum, one of the commonest species, the stem, which 

 is thickly 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. 410). The cone-like 

 flowers, consisting of the closely aggregated sporophylls, are situated in groups of 

 two or more at tlie 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 ou the upper side at the base. The sjjorangium 

 opens into two valves by a transverse slit, and lets free numerous minute s^^ores 

 (Fig. 410, //). Lycnpodium Selago differs in habit from the otlier 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 

 exine is covered with a reticulate thickening (Fig. 410, J, K). 



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

 group. The prothallia of Lycopodium clavatum (Fig. 410, A, B) and the closely 

 related L. annotinum are small white tuberous structures, which live as sub- 

 terranean sapro})hytes. At first top- shaped, they become converted by the 

 continued marginal growth into cup-shaped lobed bodies, which may attain a size 

 of two.centimeti'es. Long rhizoids spring from the lower surface, while the upper 

 surface bears numerous antheridia and archegonia. In L. coviplanatum (Fig. 411) 

 the subterranean prothalli are turnip-shaped, in L. Selago rounded or elongated and 

 cylindrical. The prothalli of the latter may be developed on the surface of the 

 soil, in which case they are gieen. In the case of L. inundatum, the prothalli of 

 which are found on damp peaty soil, and in the tropical L. cernuum, with erect 

 ])rofusely branched shoots, the prot'ialli are poor in chloroijhyll and are attached 

 to the soil by rhizoids ; they have the form of small, half-buried, cushion-like 



