of Lycopodium clavatum , L. 303 
the embryos and young plants. The question upon which 
this comparison may throw light may be stated at the outset. 
All the other Lycopodium prothalli known differ considerably 
from the L. cernuum type. Is there anything to indicate 
that they have been derived by modification of a form of 
gametophyte similar to that of L. cernuum , or do their 
characters rather suggest that, owing to the similarity of the 
mature sporophytes, a number of groups of species derived 
from independent stocks of ancient Lycopodiaceous plants 
have been grouped together in the genus Lycopodium ? The 
latter conclusion, which practically amounts to regarding the 
genus as an artificial one, is that at which Professor Bruch- 
mann arrives. It may be as well to add that this is distinct 
from the question whether the differences in the gametophyte 
are such as to justify the separation of the species of Lycopodium 
into several closely related genera. 
The prothallus of Z. Selago may be taken first, since it is 
in several respects less specialized than those of the other 
species. In form it may resemble the Z. cernuum type, being 
a short, upright cylindrical body, growing by means of a 
merismatic zone beneath the terminal region on which the 
sexual organs are borne. Being as a rule situated a short 
distance below the surface of the soil, this prothallus is devoid 
of chlorophyll, which is, however, developed in considerable 
amount on natural or artificial exposure to light. Leafy 
expansions are absent from the terminal portion, which may 
be distinguished as generative in distinction to the lower 
vegetative half. The germination of the spore is not known, 
but no distinct region comparable to the primary tubercle of 
Z. cernuum is recognizable in the fully grown prothallus ; in 
uninjured specimens this terminates below in a conical point, 
the structure of which may in some respects be compared 
with the primary tubercle. Besides this form of prothallus, 
the resemblance of which to the Z. cernuum type will be 
evident, elongated cylindrical forms which originate by growth 
becoming localized in one portion of the merismatic zone are 
found. The interest of these will be seen in connexion with 
x 2 
