346 



LYCOPODIALES 



Bl 



to its base : it is clear that the relation of the apex to the intersection of 

 the first walls has been a close one (Fig. 183 A). The axis soon proceeds 

 to form successive leaves spirally arranged. The cotyledon and subsequent 

 leaves have the ordinary characters of the foliage leaves of the species. 

 The tissue below soon becomes elongated as the hypocotyl, the length of 

 which is determined by the level at which the prothallus lies in the soil : 

 where it is at or near to the surface the hypocotyl may be quite short: 

 where deeply seated it lengthens, so that the first leaves are exposed 



above ground (Fig. 184). It is 

 traversed by a vascular strand, 

 which is monarch below, but 

 near to the first leaf, or later, it 

 becomes diarch, and shows two 

 lateral tracheidal strands. The 

 first root originates exogenously 

 from the upper tier, just above 

 the foot, and is succeeded by 

 other roots of endogenous origin 

 at higher points (Fig. 183 B). 



Here, then, is an embryogeny 

 characterised by its great direct- 

 ness and simplicity. The only 

 complication is the varying elon- 

 gation of the hypocotyl according 

 to the level of the prothallus in 

 the soil ; and there is good reason 

 to think that this is an immediate 

 adaptation to meet the varying 

 levels of development of the game- 

 tophyte in the soil, in an embryo 

 which is pertinaciously subaerial. 

 The nursing of the embryo by the 

 prothallus is not long continued, 

 nor is it structurally provided for, there being no development of an 

 elaborate "calyptra," as in some other species: the embryo soon escapes 

 from the prothallus, and fends for itself. The whole condition of the 

 embryo is such as bespeaks a simple and primitive state. Probably this 

 view would never have been in doubt had it not been for the existence of 

 different arrangements seen in other species of the genus, which happened 

 to have been described some years earlier. 



Of these the type which corresponds most nearly to L. Selago is that 

 of L. Phlegmaria, so accurately described by Treub. 1 Here the segmen- 

 tation of the embryo, as well as the origin of all the parts and their 

 proportions while young, have been fully made out, and appear to be 



1 Ann.Jard. Bot. de Buitenzorg^ vol. v., p. 87, etc. 



FIG. 183. 



Lycopodium Selago. A young embryo. X 150. 

 ^=foot ; IV.-IV. =wall separating the foot from the 

 stem-tier ; K= cotyledon ; a = apex ; .EV=suspensor. 

 B = embryo more advanced, with prothallus still attached ; 

 Z?/=cotyledon ; f^, W^ = young roots ; V=suspensor 

 attached to the foot, which is clearly defined from the 

 base of the axis. X 20. (After Bruchmann.) 



