EMBRYOLOGY 



353 





unequal growth, as in the previous case (Fig. 189 F, G). Comparing 

 the tuber of PhyUoglossum with the protocorm of L. cernuum, it is clear 

 that the relations of both to the protophylls and to the definitive axis 

 are the same : further, the relation of the foot in the embryo to the 

 protocorm is as that of the stalk to the tuber in the perennating 

 PhyUoglossum. It follows that the tuber in PhyUoglossum may be held to 

 be a " protocorm " repeated 

 annually in the life-cycle. 



In Treub's description for 

 Z. cernuum, the origin of the 

 definitive apex of the axis is 

 not brought into relation to 

 the primary segmentation of 

 the embryo. His account of 

 it is that " at the end of 

 the second phase the tubercle 

 ceases to grow, and its point 

 of vegetation gives rise to 

 the vegetative cone of a leafy 

 Lycopod-shoot," etc. 1 Nor is 

 the origin of the axis clearly 

 made out by Goebel for Lye. 

 inundatum, though its close 

 relation to the cotyledon is 

 again recognised.' 2 But the 

 continuity of existence of the 

 apex, which may be traced 

 throughout the development 

 in PhyUoglossum, suggests a 



i v T plants, showing arrangement of the protophylls. E, a plant 



Similar Continuity in L. Cer- forming a strobilus. F, G, similar plants, older, showing mode 



a,-,r] /*f/Wxr/s4 T of origin of new tuber; /= protophylls ; = apex ; / = tuber; 



nnum ana initnaatum. 1 r =root. A-EXI*. FX^. GXZ. 

 venture to think that a 



renewed investigation of the embryology of these species, especially in 

 their simpler types, would bring them into line with other Lycopods, and 

 show that the apex originates as in them from the central point of the 

 upper tier of the embryo ; but that the assertion of its characters is 

 correlatively deferred, and its identity disguised by the early prevalence of 

 the tuberous swellings and consequent irregularity of the first leaves. 



Treub's theory of the " protocorm " has already been considered in 

 Chapter XVII. Reasons were there given for not sharing the opinion 

 that the tuberous developments seen in the embryogeny of L. cernuum 

 and inundatum represent a primitive condition once wide-spread. The posi- 

 tion was not accepted that the " protocorm " embodies an early evolutionary 

 step towards the establishment of a free sporophyte prior to the formation 



FIG. 189. 



Drummondii. A, B, frontal, and side views 

 of young plant which will not form a strobilus. C, D, similar 



/,.('., p. II. 



-L.C., p. 184. 



