of Lycopodium clavatum , L. 305 
L. alpinum appears to correspond closely) does not become 
extended horizontally in this manner. It maintains an 
elongated conical shape, and the strongly convex generative 
region bears antheridia resembling those of the other species, 
and archegonia which have still longer projecting necks than 
those of L. clavatum. Here also the true neck is not very 
long, and the increased length is almost entirely due to its 
being elevated upon a ‘ false neck ’ of considerable height. 
Besides the ovum, 8-14 canal-cells are present. 
There is considerable uniformity in the appearance of the 
prothalli of the other tropical species at present known, 
L. Phlegmaria , carinatum , Hippuris , and nummularifolium y 
the main differences being in the thickness of the cylindrical 
branches, of which they consist. These ramify in all directions 
through the dead bark in which the prothalli grow. Thicker 
branches, on the upper surface of which the sexual organs are 
situated, are also found. This form suggests comparison with 
the modification of the prothallus of L . Selago referred to 
above, which was seen to arise by the localization of growth 
in one part of the merismatic zone. The early stages of the 
L. Phlegmaria prothallus are not known, and evidence is 
wanting to show whether they ever are radially symmetrical 
with a merismatic zone ; but the growth of the branches 
which bear the sexual organs shows a distinction of upper 
and lower surfaces comparable to that seen in L. Selago. The 
sexual organs themselves, which are accompanied by well- 
developed paraphyses, also resemble those of the latter 
species, the projecting archegonium-neck being entirely a 
product of the outer segment of the archegonium-mother-cell ; 
the central series consists of ovum and 3-5 canal-cells. 
It will be evident from the above description of the external 
form and the sexual organs of the known Lycopodium pro- 
thalli that they cannot on these grounds be separated into 
types unconnected by intermediate forms. The similarity in 
ground-plan of the prothalli would appear rather to indicate 
that they are all more or less profound modifications of a type 
not unlike that of L . cernuum. The two forms of prothallus 
