in Rhodymeniales : //. Delesseriaceae . 187 
species from Plymouth, suggests that temperature probably 
affects the frequency or infrequency of the female plants. 
Considering that, for the most part, male and female plants 
among Florideae are, in comparison with the tetrasporic 
plants, small and apparently depauperized, it may be that 
the cystocarpic plants are few where the conditions of tem- 
perature and illumination are favourable for vegetative 
development. It is, however, hazardous to generalize in the 
present state of our knowledge of the natural history of our 
marine Algae. 
Not more than one cystocarp usually arises on D. Hypo - 
glossum in the course of a single branch, though one cystocarp 
may often be found on each of the many proliferations of 
a branch which itself bears a cystocarp. The cystocarp 
is relatively small, and the branch persists after the cystocarp 
has discharged its spores. The procarps occur along the 
thallus in the same regular way that has been described for 
D. sanguinea and D. alata. On the female plants, at the 
proper season, every leaf-like branch seems equally to bear 
carpogonial branches throughout its course, until a cystocarp 
arises, when the production of procarps generally ceases 
(Fig. 21). 
Since the midrib does not thicken to the extent that it 
does in the species previously described, it is possible to 
detect the unfertilized carpogonial branches for great distances 
along the thallus (Fig. 22). It is moreover possible to follow 
more readily the sequence of events in the young cystocarp. 
Fig. 22 represents a surface-view of the tuft of gonimoblast- 
filaments, derived from the auxiliary cell, and the carpogonial 
branch may still be seen - in an attenuated condition lying 
alongside the tuft. No signs of a conjugation of the car- 
pogonium and the auxiliary can be seen at this stage ; though 
the incapacity of the cells of the carpogonial branch to any 
longer absorb the blue stain, which they so readily take up 
at an earlier stage, suggests that the protoplasmic contents 
have undergone change. It is fair to add that all the cells 
of the carpogonial branch behave alike in this respect. 
