Jan., 1922] NICHOLS METHODS OF HEALING IN ALGAL CELLS 23 
Cells plasmolyzed forty-five minutes or an hour after puncturing show- 
that a new plasma membrane is growing inward, cutting off a portion of 
the injured protoplasm (fig. 4, h). At the end of an hour the plasma mem- 
brane has not completely separated the plug from the protoplasm of the 
cell, as a slender protoplasmic isthmus still connects the two (fig. 4). Pre- 
vious to plasmolyzing it is impossible to distinguish any membrane or 
separation of the protoplasm near the puncture; but in plasmolysis the 
contracting membrane, drawing the plastids and pyrenoids away from the 
wall and plug, reveals the region of its formation and the extent of its growth. 
That a new membrane is formed is shown by the fact that the old membrane 
is still visible, extending across the space from the new membrane to the 
puncture (fig. 4, a). The space within the old membrane and between the 
plug and the plasmolyzed protoplasm is filled with a very finely granular 
substance, similar to cytoplasm in appearance, in which there are occasional 
coarser granules (fig. 4). At this time it is impossible to determine definitely 
whether the new membrane lines the entire cell or not, but this seems hardly 
probable in view of the later developments in the cell. Ultimately the 
membrane completes its growth, separating the plug from the protoplasm 
of the cell. As it is possible to repuncture the cell before the membrane 
has completed its growth, the hardening of the protoplasm to form the 
plug must effectively close the opening. This ingrowing membrane occa- 
sionally will form an extra loop, cutting out a deeply imbedded pyrenoid 
with its surrounding starch grains and cytoplasm. It is difficult to under- 
stand why this should occur, since this excluded pyrenoid does not appear 
different in any respect from those immediately adjacent but within the 
membrane (figs. 5, 6). 
After the new membrane has formed, the typical lamellose wall begins to 
appear. But as this wall follows the much convoluted membrane where 
it is pressed against the plug of pyrenoids and plastids, it is very irregular 
in outline (figs. 5, 6). It is very difficult to trace the new wall layers back 
against the old wall. Apparently the first layers gradually grow thinner 
as they extend back from the injury until they disappear (fig. 6, a). The 
later layers appear to line the entire cell. If the first layers are formed only 
over the plug and not uniformly over the entire cell, it would seem probable 
that they are formed by the newer portions of the membrane which is an 
outgrowth of the original membrane still lining the remainder of the cell. 
As the new wall increases in thickness it separates the old injured portion 
of the membrane from the new. 
Discussion 
The protoplasm in the different species of algae varies greatly in con- 
sistency. All degrees of viscosity can be found, from the extremely thin, 
watery fluid of Chara to the dense, viscous, slightly yellowish mass in the 
marine Cladophoras. In some species the protoplasm fails to diffuse in 
