Rhabdonia tenera , J . Ag. 423 
develops into an embryo (Whitman, ’83). On this view, the 
case of Rhabdonia , though homologous with that of Nectria 
and Sclerotinia , is not analogous with them. 
The purpose of this peculiar method of development is 
much easier to understand in the case of Sclerotinia than in 
Rhabdonia, The spores of the former germinate on the 
stigma of the host-plant, and, according to Woronin, are 
unable, when they germinate independently, to produce 
a germ-tube long enough to traverse the entire length of the 
style and reach the ovary. By uniting they are able to 
produce a much more vigorous germ-tube, which reaches the 
ovary with no difficulty. In the case of Rhabdonia the object 
seems to be entirely different : the plants produced by the 
union of four spores remain extremely small in comparison 
with those which in all probability are produced from 
a single spore. Here the object is perhaps to produce 
a large number of antheridia (the proliferations most com- 
monly bear antheridia), and so to compensate for the small 
number of antheridial plants. 
In the case of Nectria it seems natural to suppose that the 
union of several spores produces a plant which at the start 
has an advantage in competition with those plants which are 
produced from a single spore. This is probably also the case 
in the Ustilagineae. It is doubtless of advantage in the 
Florideae, and certainly seems to be so in Sclerotinia. Exactly 
what the nature of this advantage is, is not clear, but it may 
be that it claims a distant kinship with that which results 
from the fusion of two gametes, and perhaps affords a hint 
as to the mode of origin of the sexual act. 
Results. 
The frond is composed of branching filaments which grow 
by division of the terminal cells. At the growing-point there 
is a single central filament which gives off branches on 
all sides. 
The procarp is usually a three-celled branch borne on one 
F f 
