184 Phillips . — The Development of the Cystocarp 
in the same season ; and when the new proliferations arise in 
the next season, it is exclusively from the persistent midrib. 
In D. alata the plant bifurcates repeatedly in one plane by 
marginal growth near the apex ; and as the apical growth is 
apparently continuous from one season to another, the plants 
come to consist of a dichotomously branched thallus of 
considerable length. In the neighbourhood of the axils 
between the branches, it also gives rise to dense tufts of 
adventitious shoots, similar to those which come off the mid- 
rib in D. sangumea. It is on these structures for the most 
part that the reproductive organs occur ; but as far as the 
production of tetrasporangia and cystocarps is concerned, they 
also occur, but less commonly, on the surface of the ultimate 
forkings of the ordinary thallus. Hence it would seem that 
D. sanguined is a more highly specialized plant than D. alata. 
The apical growth of the thallus is as pronounced in this 
species as in the other, and no true intercalary growth occurs 
throughout its structure. D. alata has been selected by Kny 
(’86) in his well-known ‘ Wandtafeln , for illustration of apical 
growth. Wille (’87), in his figures of the apex, seems to 
consider that cells of the axial row divide by means of 
c horizontal ’ walls, i. e. by transverse divisions, which is not 
the case. The so-called ‘ hyphal * cells which arise from the 
inner cells some distance behind the apex in D. sanguined 
occur also in this species. Wille regards their function here 
as that of conduction, not of storage. 
The young axillary proliferations of D. alata serve well for 
the study of the development of the cystocarp, as in the same 
tuft there may be found varying stages of growth. The 
cystocarp arises on the midrib some distance behind the apex, 
and gradually enlarges as a papillar elevation until it can 
be seen in profile by means of a hand-lens. The mature 
cystocarp, however, never so completely transforms the 
appearance of the branchlet as it does in D. sanguined. This 
is partly because the cystocarp is not so bulky, and partly 
because the proliferation is in the end larger than those of 
D. sanguined. 
