383 
Alga-like Organism. 
which the protoplasmic mass remains quiet, at the end of the 
filament, long enough for one or more cross-walls to be formed 
at its inferior end. The periods of rest occur at such intervals 
of time that the cross-walls divide the filament into empty 
compartments, which are remarkably uniform in size and are 
about the same length as the masses of protoplasm. 
Now that we have seen how the zoospores germinate, and 
understand the principal characteristics of the peculiar mode 
of growth, we can return to the green cells at the ends of the 
branches of adult plants, and consider a peculiarity of structure 
that was not treated in detail in the first part of the paper. 
This is the manner in which the inferior ends of the masses of 
protoplasm frequently extend downwards in the form of pro- 
cesses (see Fig. 2), which are closely applied against the wall 
of the filament. These processes contain portions of the 
chromatophore, but the extreme ends are usually hyaline. 
They are only to be found when the protoplasmic masses 
have left the quiet condition, and the filament is actually 
elongating. They are really but an exaggeration of the 
undulating contour of the inferior ends of the protoplasmic 
masses in young plants, when the latter are in the period of 
active growth. 
The contents of a cell having these protoplasmic processes 
are very sensitive, and if, when living material is examined, 
the normal conditions are not carefully maintained, these pro- 
cesses are drawn in, the protoplasmic mass contracts, and the 
posterior end becomes rounded off. Thus when specimens were 
observed on a slide in salt water, this contraction of the cell- 
contents invariably occurred in the course of twenty to thirty 
minutes, apparently because the evaporation of the salt water 
under the cover-glass altered the density of that fluid. Similar 
specimens confined in a Van Tieghem cell were much less 
sensitive, and might be observed for a much longer time with- 
out detecting any such change, although the masses of proto- 
plasm never continued their forward growth, and always 
eventually contracted into the form commonly assumed when 
a cross- wall is to be formed. 
