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. 



