IIo BOTANICAL GAZETTE [AUGUST _ 
more or less completely embryonic, rhust be connected with certain 
differences in the metabolic processes in the two groups. Morpho- 
logical structure in the animal is to a large extent primarily colloid 
and protoplasmic, while in the plant the structural substances are 
mainly carbohydrates, and the protoplasm itself shows little per- 
_manent or persistent structure. Apparently in plant metabolism 
the proteids and other protoplasmic substances produced are less 
stable under physiological conditions than in the animal, and so 
do not persist as structure but are continually undergoing change 
and reconstitution, particularly in regions of high metabolic activity. 
In the animal, on the other hand, some relatively stable molecules 
arise even in regions of the highest activity; consequently mor- 
phological structure appears, even in these regions, and such struc- 
ture is more stable than structure developed in regions of lower 
metabolic rate. Because of these differences the apical region of 
the animal undergoes differentiation, and its relations to other parts 
determine that this differentiation shall take the form of a trans- 
mitting system, the nervous system, which brings about a high 
degree of physiological integration, while in the plant the apical 
region usually remains embryonic or differentiates very slowly. 
Transmission exists only in relatively primitive form and the degree 
_of physiological individuation in the plant remains low. 
In the unicellular hairs of Ceramium and Champia the suscepti- 
bility gradient is usually acropetal in the full grown hairs, but 
apparently basipetal in the growing hairs and in the multicellular - 
branching hairs of Chondriopsis the gradient of the hair as a whole 
is basipetal while that of single cells is acropetal in the full-grown 
hairs. In the multicellular hairs of Castagnea the gradient is usually 
basipetal, but a distinct intracellular gradient could not be dis- 
tinguished. Further work is necessary for positive conclusions, 
but a suggestion is perhaps permissible. These hairs of course 
are incapable of photosynthesis and are dependent, therefore, on 
other parts of the plant for nutrition. The course of nutritive 
substances must therefore be acropetal in direction in them. In 
view of the facts available, it seems probable that during the 
growth of the hair the apical region has the highest metabolic 
