100 BOTANICAL GAZETTE [AUGUST 
thalli where growth is no longer apical but more or less generally 
distributed, cells here and there have undergone more or less dedif- 
ferentiation, and so have become younger and resumed reproduc- 
tion. 
Where a thallus has been broken or injured, an area of high 
susceptibility extends for a greater or less distance, often o. 5 mm. 
or more from the region of injury. In the younger portions of the 
thallus where the basipetal gradient is still present, this area of high 
susceptibility arising from an injury extends farther in the basal 
than in the apical direction. Evidently this area represents the 
extent of the stimulation resulting from the injury, or at least the 
more persistent component of it. 
The visible changes in the single cells as death approaches are 
essentially those described in the preceding section. First the 
color of the stain deepens, beginning in the young branches at the 
apical end and proceeding basipetally. Then as the protoplast 
undergoes disintegration and coagulation at death, the cell con- 
tents appear as an irregular blackish mass, but from this the color 
soon disappears and the dead decolorized cell is yellowish green 
instead of green under low powers, while under high powers the 
coagulated masses of protoplasm are visible. 
The susceptibility method can undoubtedly be used for analyz- 
ing the metabolic conditions in Enteromor pha and related forms to a 
much greater extent than the few experiments described here 
indicate. As regards the question of metabolic gradients, however, 
these experiments give a definite answer. They show that the 
vegetative individual is dynamically in its earlier stages such a 
gradient, that each new branch is a new gradient and so a new 
individual, and that with advancing age and under certain 
environmental conditions the gradient may disappear more or 
less completely and give place to a mosaic of more active regions 
scattered over the thallus or more distinct basally. 
Ectocarpus confervoides.—In this form the branches which are 
younger as regards development and the more apical regions of 
most others show a distinct basipetal gradient, while in the more 
basal regions of the more advanced parts of the thallus con- 
siderable irregularity appears, some cells dying earlier or later than 
6 
