Pteridophytes. Are they vestigial ? 247 
tubercle’ recognized in L. cernuum was regarded as a foot, 
which had escaped from the prothallus : it is still spoken of 
by Bruchmann 1 in that way, and the type of embryo of 
L. inundatum is described as ‘ freifiissig,’ in which the 
embryonic foot is developed outside the prothallus. But 
Treub showed that the embryonic tubercle is not of the same 
origin as the intra-prothallial foot : the latter originates from 
the first or lower tier of the embryo, the tubercle from the 
upper, which gives rise also to the cotyledon and stem. The 
embryonic tubercle, thus shown by origin not to be the true 
foot, was regarded by Treub as an organ which played an 
important part in the passage of the sporophyte to a state of 
physiological independence. He regards it as a primitive, 
not a reduced structure, and introduced the term ‘ protocorm,’ 
recognizing in it a preliminary stage of development of the 
young Lycopod plant. Those cases in which no obvious 
protocorm is developed are explained on the ground of its 
disappearance, and because of their epiphytic saprophytism 
(Z. Phlegmaria , carinatum , Hippuris , nummularifolium) they 
are held to be more recent types than those which show a 
protocorm. Naturally in Phylloglossiim the tuber itself is 
regarded as a protocorm, repeated over and over again, and 
on Treub’s theory of the protocorm it would thus take a place 
as an embryonic type still playing a considerable role. 
But now the question is, How will the embryology of 
L. Selago fall in with this view? It is a ground-growing 
species, in which neither the prothallus nor the sporophyte 
are highly specialized. But the protocorm is absent, there 
being no swelling at the base of the hypocotyl until the 
appearance of the first root. These facts seem to me to 
necessitate a reconsideration of the protocorm and protophylls : 
are they really primitive structures, general in the ancestry 
of all Lycopods, or the result of a vegetative adaptation, 
which has made its appearance in certain species only; formed 
early in the individual plant, but relatively late in the phylo- 
geny ; and not a general character for the whole race ? 
1 Bruchmann, loc. cit., p. 102. 
