1916] CHILD—GRADIENTS IN ALGAE 103 
meters from the apical ends when the plants are in good condition. 
In the more basal regions of the older, highly branched thalli, 
however, more or less irregularity usually appears, death occurring 
at the same time over lengths of 2 or 3 mm., or certain levels of the 
stem showing a higher or lower susceptibility than adjoining regions. 
Many very young unbranched individuals of C. rubrum, ranging 
from only 6-8 to 30-40 cells in length, which were found growing 
on other algae, were examined in situ and therefore in wholly intact 
condition. In-these the basipetal susceptibility gradient was 
found to be very regular, and in the shorter individuals it extended 
to the base of the plant, while in some of the longer, some slight 
irregularity appeared in the basal region.. As might be expected 
from the dichotomous branching in Ceramium, the susceptibility 
of all apical regions from the same general portion of a highly 
branched thallus was found to be about the same, except that in 
various cases where one member of a pair of young branches had 
been retarded in its development, the susceptibility of the retarded 
member was slightly less than that of the other. Different regions 
of the thallus, however, may show. somewhat different suscepti- 
bilities even in the apical regions. For example, the lower periph- 
eral portions of a large, highly branched thallus are often less 
susceptible than the upper parts, probably in consequence of differ- 
ent environmental conditions. C. rubrum is rather resistant to 
laboratory conditions as compared with other forms; the apical 
regions retain their susceptibility and the gradients persist with 
little or no change, even after a day or two in standing water. 
The differences in susceptibility along the axis in C. rubrum are 
such that it requires several hours in KCN m/1oo for death to 
progress from the growing tip to a level 3-4 mm. below it. In 
young unbranched plants about 20 cells in length, the progress of 
death over the whole length of the plant required about an hour 
in cases observed. In a few cases the progress of death from cell to 
cell was followed and timed for some distance. In the younger 
plants and the more apical regions of older axes the length of time 
between the death of one large cell of the axis and the next basal 
to it is only 2-3 minutes, while in more basal regions, where the meta- 
bolic rate is lower, it may be 15-20 minutes. The collapse and 
