526 



BOTANY 



PART II 



f 



group. The prothallia of Lycopodium clavatum (Fig. 491 A, B) and the closely 

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

 terranean 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. The spores only germinate after 

 six to seven years, forming at the expense 

 of their reserve materials a prothallus of five 

 cells. Further development only takes place 

 when fungal hyphae enter the lowest cells 

 (Fig. 492 A, S). The endophytic fungus 

 is confined to the peripheral tissues of older 

 prothalli ; it may emerge through the special- 

 ised basal cells of the rhizoids and invest 

 the latter ( 125 ). Only after twelve to fifteen 

 years is the prothallus sexually mature, so 

 that its life may last some twenty years. In 

 L. complanatum (Fig. 492 (7) the subterra- 

 nean prothalli are turnip-shaped, in L. Selago 

 rounded or elongated cylindrical and dorsi- 

 ventral. The prothalli of the latter may be 

 developed on the surface of the soil, in which 

 case they are green. In the case of L. inun- 

 datum, the prothalli of which are found on 

 damp peaty soil, and in the tropical L. cer- 

 nuum, with erect profusely-branched shoots, 



the prothalli are poor in chlorophyll and are 

 FIG. 493. Development of the embryo in 



Lycopodium conplanatum. A, Embryo attached to the soil by rhizoids ; they have 

 showing the first divisions ; the basal the form of small, half-buried, cushion-like 

 wall / separates the suspensor (et) from masses of tissue, which give rise to green, 

 the body of the embryo; the transversal aedal tha n o id lobes. The archegonia occur 

 walls II and /// (the latter being in the , ,-, > c j-u i -U ii j-v j ^ 



plane of the section) together with the at the base of these lobes > the ^theridia also 

 transverse wall IV give rise to two tiers on their surface. All Lycopod prothalli have 

 of four cells ; the tier next the sus- fungal filaments forming a mycorrhiza in their 

 pensor gives rise to the foot, the ter- peripheral tissue. 



minal tier forms the shoot, (x 112). E ^ prothallia are all monoecious. The 

 Embryo of medium age ; s, apex of 



stem; b, rudiment of leaf ; /, foot (x antheridia are somewhat sunk in the tissue 

 112). C, Embryo shortly before break- (Fig. 491 C) and enclose numerous spermato- 

 ing out of the prothallus ; bb, the two zo [^ mother-cells, in which small oval spenna- 

 first leaves covering the apex of the tozoid with two cilia attached below the 

 stem; w, the first root (x 40). (After . 



BRUCHMANN.) apex, are formed. The archegonia (Fig. 491 



E, F) are constructed like those of the Ferns, 



but the upper cells of the neck become disorganised on opening. The number 

 of neck-canal-cells differs in the various species (1, 3-5, or 6-10). 



The embryo (Fig. 493) remains during its development enclosed in the 

 prothallus. It has a spherical, in L. complanatum club-shaped and irregular, 

 foot which serves as an absorbent organ for the sporeling. Beneath the foot the 

 young shoot forms ; the first leaves are scale-like, and from the basal portion of 

 the shoot the first root develops. The suspensor is situated between the shoot 

 and the foot ; it serves as the first absorbent and nourishing organ of the embryo. 



B 



