1916] CHILD—GRADIENTS IN ALGAE 107 
whether young actively growing hairs will show the two opposed 
gradients or not. Discussion of the facts is postponed to the general 
section of the paper. 
Polysiphonia variegata and P. fibrillosa—In P. variegata the 
general axial gradient is clearly basipetal in each axis, with a few 
irregularities in freshly collected plants. The transparent, dichot- 
omously branching hairs also show a basipetal gradient, both 
in the hair as a whole and in the single cells, so far as observed. 
After a day or two in the laboratory irregularities in the suscepti- 
bility are much more frequent. 
Cystocarps in various stages of development were present on 
some of the plants examined, as in Chondriopsis. The cystocarp 
wall shows a basipetal gradient. In general the susceptibility 
of the cystocarp, except in the earliest stages of its development, is 
lower than that of the cells of the vegetative axis from which it~ 
arises, and it was further noted that the region of the branch to 
which the cystocarp is attached also shows a lower susceptibility 
than adjoining regions of the axis. This low susceptibility may 
extend basipetally over 4 or 5 segments of the thallus, and acro- 
petally over 2 or 3, and is more marked in connection with more 
advanced than with earlier cystocarps. Apparently the cystocarp 
in its later stages, together with a portion of the vegetative thallus 
in the region of its attachment, represents a region of lower meta- 
bolic activity than the adjoining vegetative regions. 
As in Chondriopsis, the cystocarp contents in the earlier stages 
are much more susceptible than the fully developed carpospores 
which are the least susceptible portions of the whole plant on which 
they occur. Apparently metabolic activity in the carpospores 
is relatively slight. 
P. fibrillosa is in general much more susceptible then P. variegata, 
and after a few hours in the laboratory the course of death along 
the axes is very irregular. In freshly collected plants, however, 
a basipetal gradient usually appears clearly in the more apical 
regions, but even here the irregularities are very frequent a few 
millimeters from the tips, and sometimes death occurs first at some 
level below the tip. I think it probable that these irregularities 
result from stimulation or injury of the apparently very sensitive 
