EMBRYOLOGY 



349 



its greatest development is nor> always in the plane of the median wall, 

 but on that side from which the greatest quantity of nutriment flows from 

 the prothallus, and this brings about a torsion which the suspensor does 

 not prevent. In fact, the "foot" is here an opportunist growth, inconstant 

 in position itself, and distorting in a variable manner the rest of the embryo. 

 Soon after the origin of the first two leaves follows the origin of the first 





FIG. 1 86. 



A young embryo ot Lycopodium annotinum. I.-I. =the basal wall; Il.-II. =the 

 transverse wall; IV. -IV. =the wall separating the foot-tier from the stem-tier. Z? = an 

 older embryo of L. clavatum, showing more advanced development of the two tiers, and 

 especially of the foot-tier. L =an older embryo detached, with cotyledons (BJ i), a further 

 leaf (Biz), and the firsj; root (W), and foot (F). D young underground, colourless 

 seedling ; ^=foot ; JV=root ; /F 2 = origin of a second root ; Bl leaf-scales, of which the 

 first pair are the cotyledons. A and 2>X 150. 0x52. DX.IO. (After Bruchmann.) 



root, in a position variable relatively to them (Fig. i86c). The embryo 

 then bursts the tissue of the prothallus, as a consequence of active inter- 

 calary growth of the hypocotyl, which emerges upwards, while the root 

 enters the soil downwards (Fig. 1860). The axis while growing through 

 the soil is pale, and bears only colourless scale-leaves, but on emerging 

 ultimately at the surface these pass into green leaves of the ordinary foliage 

 type (Fig. 179 A). The embryology thus described is more complex than 

 that of the Selago type : its details are plainly in accordance with the 

 saprophytic specialisation of the prothallus, and with its position deeply 



