22 AMERICAN JOURNAL OF BOTANY [Vol. 9 
the pyrenoids and proteid bodies excluded and those retained by the new 
membrane. After twenty-four hours the membrane is completely formed 
over the base of the plug, and a thin film of wall is developed. This new 
wall can be traced at this time only for a short distance from the opening, 
where it gradually grows thinner and finally disappears. It thickens very 
slowly, for after three days it is only slightly more pronounced; though by 
this time the membrane or, rather, the new wall layers appear to extend 
farther outward from the wound over the cell. Ultimately the new wall 
encloses the entire cell, and the healing of the wound is completed as in 
Chaetomorpha. 
Chaetomorpha melagonium f. typica (Web. & Mohr) Kiitzing. This 
marine Chaetomorpha was also a very satisfactory form for study. The 
material occurred in great abundance among the fronds of Chondrus crispus, 
and was eas}^ to collect at low tide. The large size of the cells, the character 
of the cell wall, and the fact that it grows well in culture were factors de- 
termining the selection of this species. 
The cell walls are tough, elastic, thick, and striated; and their inner 
surfaces are very finely corrugated. The corrugations usually run in a 
slightly spiral manner from one end of the cell to the other. They do not 
appear to be formed by overlapping lamellae, such as West and Hood ('ii) 
found in Trentepohlia, but are rather slight folds of the inner membrane. 
The turgid condition of the cells and the elasticity of the walls are 
essential factors in piercing these tough, pliable walls. When the needle 
is withdrawn, the contents of the cell slowly flow out and diffuse through 
the water. There is no surface film formed over the protruding protoplasm, 
as in the case of Nitella and many other algae; but the protoplasm, together 
with the chloroplastids, starch grains, and other particles, spreads through 
the water until it is no longer possible to trace them. Removing the needle 
causes a slight current in the water, which aids in scattering the particles 
and also determines the direction of their more rapid dispersal (fig. 2). 
Finally the starch grains and plastids accumulate at the opening until a 
plug is formed and all movement ceases. This plug seems to harden, and 
thus effectually closes the hole; and the cell may be repunctured in forty- 
five minutes or an hour, according to the size of the hole. The great 
elasticity of the wall is doubtless a material aid in checking the outflow. 
The extreme elasticity of these walls is strikingly illustrated if a cell is 
cut across one end, when the wall frequently contracts until the lumen of 
the cell is reduced to two thirds or even one half its original diameter. 
At the end of two or three hours all the exuded contents have disappeared 
with the exception of a small, indefinite, discolored mass immediately over 
the opening; finally, after two or three days, this also disintegrates. The 
internal plug is still evident, but gradually grows less and less pronounced 
until it is difficult or impossible to locate the smaller punctures. The 
larger punctures (200-300 microns) are still visible at the end of a month, 
although less conspicuous than during the first week. 
