1916] CHILD—GRADIENTS IN ALGAE 105 
conditions, I am inclined to regard this species as rather sensitive 
and readily injured physiologically, and such a high susceptibility 
would readily account for the irregularities observed in the death 
gradient. 
Champia (Chylocladia) parvula—Various stages of develop- 
ment, ranging from unbranched to large much branched thalli, 
were examined. In general, death begins at the apical end of each 
axis. A short terminal portion, evidently representing a growing 
tip, dies first, and then, after a more or less distinct interval, death 
proceeds slowly basipetally. In the younger, shorter axes the 
gradient is usually very regular over most of the length, and in the 
older axes over the apical 2~3mm. Farther basally, however, 
irregularities appear in cells or cell groups. Whether these irregu- 
larities indicate physiological isolation and secondary growth in 
these basal regions, or whether they are the result of injuries or 
other external factors, I do not know. They are certainly more 
frequent in the longer, older axes than in the shorter, younger ones. 
In general also the younger axes, or at least their more basal regions, 
show a higher susceptibility than the older axes, so that while the 
death of the growing tip may occur at about the same time in both, 
the basal region of the younger branch may die considerably earlier 
than that of the older branch. 
The transparent, unicellular hairs which develop on the thallus 
usually show an acropetal susceptibility gradient in the cases 
examined, like the hairs of Ceramium rubrum, although in some 
hairs the gradient is basipetal and in some death begins at both 
ends and proceeds toward the middle. Further observations are 
necessary to determine with certainty the meaning of these dif- 
ferences, but it seems probable that, as in Ceramium, the growing 
hair may have a basipetal gradient, the full grown hair an acropetal 
gradient, and that those in which death begins at both ends are 
Stages in the change from one condition to the other. It may be, 
however, that stimulation or injury is responsible for these dif- 
ferences in some cases at least. 
Chondriopsis (Chondria) dasyphylla var. sedifolia—In young 
unbranched or slightly branched plants in good condition and 
usually in the more apical regions of the branches in older much 
