Review. 
223 
Mr. Holloway keeps an open mind on the vexed question as to 
whether the protocorm is a late specialization or a highly primitive 
organ. He remarks that at first sight the case of L. laterale might 
seem to afford an argument in favour of the latter view, for the 
protocorm here “ by no means bears the character of a mere 
temporary organ ”; but he adds that it might be urged with 
considerable reason that the “ pt'otocormous rhizome ” of L. laterale 
may be “ merely a physiological specialization, peculiar to this 
species,” designed to carry this marsh-loving form over an 
unsuitable season. Without entering fully into the difficult 
controversy concerning the nature of the protocorm it may be 
well to recall that Professor Bower in his later works regards the 
protocorm not as a persistent relic from a remote ancestry but as 
a parenchymatous swelling of the nature of an opportunist growth; 
he compares it to the foot, drawing the conclusion that the Lycopod 
embryo seems prone to parenchymatous swelling (2). Other writers 
hold the view, first set forth by Treub, that the protocorm is the 
phylogenetic precursor of the stem, a view once also held by 
Professor Bower (1, 6, 7). In the face of Mr. Holloway’s demon¬ 
stration that vascular tissue penetrates for some distance in the 
protocorm of L. laterale this organ cannot, at least in that species, 
be dismissed as a mere parenchymatous swelling. Further, it is 
difficult to deny the probability that the protocorm of L. laterale 
had the same origin as those of L. cernnum and L. inundatum, for 
all three species show close relationship in their prothalli and 
general structure. But are we, therefore, bound to accept the 
protocorm as the primitive form of the stem, the precursor of the 
ordinary form of Lycopodinous axis? I think not. It is true that 
Dr. Lang has shown that the type of prothallus with which the 
protocorm is associated is probably primitive and there seems an 
inherent probability that the gametophyte, often relatively long-lived, 
might influence the embryology of the young sporophyte. But in 
the face of the enormous development of the stem in the oldest 
fossil Lycopods known to us and of the essential histological 
similarities of the stem throughout the phylum of the Lycopodiales 
the probability that the protocorm is a modified form of stem, due 
to reduction, at once suggests itself and this view is supported by 
the late development of vascular tissues in the Lycopodiaceas. If 
the protocorm is a reduced form of the stem it is quite natural that 
in L. laterale where this reduction is much less than in the other 
species of Lycopodium some vascular tissues should persist. It is, 
of course, possible to regard the protocorm of L. laterale as the last 
term in a series of swellings, at first parenchymatous in nature but 
later developing vascular tissue in accordance with their opportunist 
nature. But that stems may by shortening and reduction assume 
a protocorm-like form is shown among the Pteridophyta by the 
recently described case of a protocorm in Ophioglossuin vulgatum 
(6). This protocorm has, it is true, little in common with 
that of the eligulate Lycopods except outward form ; for it is 
provided with a vascular system comparable in all essentials to 
that of the rhizome, except that owing to unequal growth of the 
upper and lower parts of the segments of the apical cell the vascular 
system has become turned inside out and everted, the apical 
