714 THE AMERICAN NATURALIST. . VoL. XXXIX. 
groundwork of trophoplasm, whether fibrillar, granular, or pre- 
senting the structure of foam, botanical science has as yet fur- 
nished very little systematic study and this field of research is 
one of exceptional opportunity for the student of the plant cell. 
The Cell Wall— The cell wall may be treated from two 
points of view : either with respect to the strict chemistry of its 
organization and development or more largely for the biological 
and morphological features involved. The chemistry of the cell 
wall is an exceedingly complex subject which has developed a 
special literature of its own. In the substance termed cellulose 
we are not dealing with a single body but rather with a large 
group of closely related bodies. And besides the members of 
the cellulose group there may be present foreign substances so 
intimately associated with the carbohydrates as to resist very 
severe treatment. We cannot even touch this phase of the sub- 
ject ; a brief review of its complexities and problems is presented 
by Beer (:04) and there are further references in Section I of 
these “ Studies." : 
There are, however, some biological features of the process of 
wall formation, the morphological and physiological aspects of 
the phenomena as they are related to protoplasm, which offer 
some exceedingly interesting problems especially among the 
thallophytes. It has long been a matter of dispute whether the 
cell wall is a secretion from the surface of a plasma membrane 
or is formed wholly or in part by the transformation of such a 
membrane. 
It seems to be established now that substances of the cellu- 
lose groups are only formed in contact with plasma membranes, 
that is, they are not formed actually in the interior of proto- 
plasm although they may appear to lie in such situations. Thus 
the material of the capillitium of the Myxomycetes which is of | 
the same character as the chief substance in the exterior cover- 
ing of the fructification, is laid down within vacuoles in the 
protoplasm, and is therefore in contact with the surface of vacu- 
olar plasma membranes precisely as the outer covering lies in 
contact with the surface of the outer plasma membrane. The 
morphological relation of capillitium and outer covering to the 
surface of plasma membranes is therefore precisely the same. 
