THE STRUCTURE OF PROTOPLASM 
287 
of the cell illustrates especially well the conception of cell structure which 
implies differentiated regions of a colloidal system in which special pro- 
cesses have "become localized and tend to remain fixed. I have endeavored 
in my discussion of the conceptions of the cytologist as to cell structure to 
present them as far as possible from the standpoint of our present concep- 
tions of the protoplasm as a polyphase colloidal system or complex of such 
systems. We may turn now to the more specific discussion of the influence 
which the new discoveries in the chemistry of the colloidal condition has 
had on our conception of cell structure. 
Data from the Chemistry of the Colloidal Condition 
The contributions arising from the modern study of matter in the col- 
loidal condition to our conceptions of protoplasm have been, in my opinion, 
of the most far-reaching significance. We can perhaps appreciate most 
fully the change in the relations of biology and chemistry which has come 
with the development of the chemistry of the colloids if we consider the 
contributions of chemistry to that oldest and most elusive of biological 
problems — the nature and origin of adaptive form. It is here perhaps in 
the problems of morphogenesis that chemistry has appeared most helpless 
and the biologist has felt most justified in resorting to mystical and vitalistic 
conceptions of regulative principles, developmental tendencies, etc. I have 
referred above to our inability to conceive how the chromosomes as bearers of 
the hereditary characters can control the development of the inherited form 
characters in ontogeny. 
The attempt to explain the form of organisms on the basis of analogies 
with crystalline forms and configurations has failed so conspicuously that 
biologists might well perhaps feel justified in questioning the possibility 
of a chemical theory of plant and animal form. A glance at the older and 
the more recent attempts in this direction is perhaps of interest. 
Grew in 1672 felt the necessity of attacking the problem of the causation 
of plant forms from the standpoint of the forms of the crystals of salts 
found in plant juices. Out of the few and simple crystal types which he 
could isolate he put together groups which were supposed to explain the 
development of the trunk, the divergence of branches from the main axis 
at various angles, the serration of leaf margins, the formation of spiral 
vessels, and, to Grew most important of all, the very method by which the 
"fibers" are spun together to form the cell walls in Dame Nature's endless 
weaving of the lace-Hke patterns of the plant tissues. This was in 1672 and 
dates the beginning of the cell theory. In 1903 Przibram, undeterred by 
the failures of three hundred years, again claims to lay the foundations of a 
true theory of morphogenesis by a comparison of form development in 
both plants and aaimals with the growth, twinning, regeneration, etc., of 
crystals. He compares the replacement of a broken-off angle of a crystal 
to the regeneration of a salamander's leg and the replacement of a leaf tip. 
The bifurcation of a fern frond looks to him like the twinning of a crystal. 
