354 LYCOPOD1ALES 



of a root. An alternative view was there propounded that the Lycopod 

 embryo is a body prone to parenchymatous swelling, and that the 

 "protocorm" is a consequence of secondary specialisation. It remains to 

 group the facts of embryogeny in the eligulate Lycopods in accordance 

 with that alternative view. 



The simplest type of embryogeny in the genus is that of Z. Selago, 

 a species already recognised as primitive in the characters of the sporophyte. 

 The embryo accommodates its growth in length to the level of its parent 

 prothallus ; excepting for this the embryo is of a constant type, without 

 any complications of parenchymatous swelling. I regard this as a primitive 

 condition for the genus, and the main features are these : a suspensor 

 and foot of moderate size, passing directly into the primitive shoot, which 

 escapes early from the prothallus, and expands its first leaves as green 

 assimilating leaves. The apex of the axis, which provides a definite leaf- 

 succession, is established early at the centre of the upper tier ; the first 

 root is formed early and exogenously, and it is followed soon by others of 

 endogenous origin. Thus the young plant is simply and directly set up 

 as an independent unit (Figs. 183, 184). The type most nearly corre- 

 sponding to Z. Selago is that of Z. Phlegmaria. Notwithstanding the pro- 

 nounced saprophytism of the prothallus, the embryogeny is practically 

 identical in all essentials with that of Z. Selago, though more exactly 

 worked out (Fig. 185). But it is different with the davatum-annotinum-\y^e. 

 Here the primary embryogeny is the same as in Z. Phlegwaria, but the 

 deeply underground position of the saprophytic prothallus necessitates longer 

 and more efficient nursing of the embryo before it can establish its 

 physiological independence. The absorptive surface and storage capacity 

 of the embryo are accordingly enlarged by parenchymatous swelling of 

 the foot. The directness of the adaptation is here indicated' by the fact 

 that the enlargement is on whatever side is nearest to the greatest source 

 of supply. The late differentiation of the several parts, and the tardy 

 emergence of the embryo from the prothallus, are all in accord with the 

 necessarily longer nursing period : while the colourless scale-character of 

 the earliest leaves is also a natural and secondary consequence of the 

 subterranean embryogeny. It is not difficult to see in the clavatiim-\ypz 

 an embryogeny essentially like that of Selago, but secondarily modified in 

 relation to the subterranean habit of the prothallus. This accords well 

 with the fact that the species included are more highly specialised than 

 Z. Selago as regards the characters of the sporophyte (Fig. 186). 



The ctrnuum-inuhdatum-\ypz on general characters of its prothallus and 

 sporophyte takes a middle position. The embryogeny opens as in other 

 Lycopods : but the foot-tier, which is enlarged in the davatum-\y^z, here 

 remains small. The origin of the cotyledon is as in Z. Selago, but the 

 swelling in the upper tier, which begins early on the side directed down- 

 wards, profoundly disturbs the subsequent arrangements, so that detailed 

 comparisons become difficult, and, as a consequence, the origin of the axis 



