302 Lang . — The Prothallus 
There are several reasons which appear to indicate that 
the type of prothallus, the main characters of which, as 
described by Treub and Goebel, have been summarized above, 
is in some degree a primitive one. Whether it is to be re- 
garded as primitive in relation to the other types of Lyco- 
podium prothallus is a further question that will be considered 
later. In the first place the prothalli of the L. cernuum type 
possess chlorophyll, and are thus capable of assimilation, 
though the presence of an endophytic Fungus probably indi- 
cates that some degree of saprophytism is possible in addition. 
But more direct evidence is supplied by the form of the young 
sporophyte. The parts of this which have been mentioned, 
viz. protocorm, leaves borne on the protocorm, leafy shoot and 
exogenous first root, afford when taken together characteristic 
marks which may fairly be used for phylogenetic purposes. 
They are repeated exactly, not only in all young plants 
arising from the fertilized ovum, but in those which originate 
vegetatively. These are known in the case of L. inundatum 
to arise from leaves separated from the young sporophyte, 
and in L. cernuum from the ‘ root-tubercles/ the further 
development of which agrees with that of a young protocorm. 
Further, a close correspondence can be traced between the 
development of plants of L. cernuum from the root-tubercles 
and the vegetative propagation of Phylloglossum Drum - 
mondii \ which may on other grounds be regarded as a 
primitive form. Even in the absence of any information as 
to the gametophyte in this genus, this resemblance affords 
important evidence that the form of the young plant of 
L . cernuum , &c., is not to be regarded as recent and adaptive, 
but as possessing an important phylogenetic bearing. 
The prothalli and young plants of L. Selago , complanatum , 
and clavatum , and those which present the type of L. Phleg- 
maria , may now be compared with the L. cernuum type. 
It will be convenient to deal in the first place with the 
external form, sexual organs, &c. ; then to consider the differ- 
ences of anatomical differentiation ; and lastly to compare 
1 Bower, Phil. Trans., 1885, p. 675. 
