298 Phillips . — On the Development of 
equivalents. In Polysiphonia nigresceyis the antheridia and 
procarps are modified leaves branching beyond the fertile 
region in the same manner as the ordinary leaves branch. 
The formation of the cystocarp corresponds in every essential 
particular to that already described for Rhodomela subfusc a. 
The cell-divisions constituting the pericarp may be followed 
with greater ease in this species than in Rhodomela subfusca. 
Speaking generally, it may be said that the ecorticated species 
of Rhodomelaceae have a more simply-formed pericarp than 
have the corticated species. The origin of the paranemata 
in a pair of cells derived laterally from the central cell may 
be clearly traced ; though I believe I have seen that, in the 
median line below, a row of paranematal cells is derived from 
a pericentral cell of the first joint, forming the stalk of the 
cystocarp. The subdivision of the auxiliary cell after fertili- 
zation into a superior sporogenous and an inferior sterile cell, 
I have only been able to see rarely. The difficulty arises 
from the fact that a much larger number of carpospores is 
formed in this species than in Rhodomela subfusca. This 
dense * nucleus 5 consisting of from ten to twenty times as 
many spores as occur in Rhodomela , obscures the changes 
taking place at the core of the fructification. The greater 
drain upon the resources of the sporogenous cell due to the 
formation of a large number of carpospores, probably accounts 
for a phenomenon which distinguishes this species from the 
other. I refer to the apparent retrogressive absorption by 
the sporogenous cell of the auxiliary cell and later, of all 
its sterile derivatives, leaving in its place a large multipolar, 
multinucleate sporogenous mass, which may be occasionally 
squeezed out from nearly ripe cystocarps, and two of which 
I figure (Figs. 11, 12). I have never been able to see such 
absorption in Rhodomela subfusca , and it is certain that in 
that species the auxiliary cell and all its sterile derivatives 
remain at a relatively late period of spore-formation. In 
Polysiphonia nigrescens , on the other hand, I have failed to 
trace the sterile elements when once spore-formation has 
well set in. 
