EMBRYOLOGY 353 
unequal growth, as in the previous case (Fig. 189 F, G). Comparing 
the tuber of Phy//oglossum with the protocorm of ZL. cernuum, it is clear 
that the relations of both to the protophylls and to the definitive avxis 
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 
Phylloglossum. It follows that the tuber in Phydlog/ossum may be held to 
be a ‘“‘protocorm” repeated 
annually in the life-cycle. 
In Treub’s description for 
L. 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.! Nor is 
the origin of the axis clearly 
made out by Goebel for ZLyc. 
inundatum, though its close 
relation to the cotyledon is 
again recognised.? But the 
continuity of existence of the 
apex, which may be traced 
throughout the development 
in Phylloglossum, suggests a Boole nh ae mee) e Psbesies ane nee 
Rees i 3 s plants, showing arrangement of the protophylls. E, a plant 
similar continuity in Z. ce7- forming a strobilus. 7, G, similar plants, older, showing mode 
mii and tandanon: I of origin 2 ce eile tes a@=apex; ¢=tuber ; 
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 ZL. cernuum 
and znundatum 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 
UD Gis Be Ts 2 Lec, p. 184. 
