III. FINE-STRUCTURE 

 OF PROTOPLASMIC DERIVATIVES 



The distinctive feature in the structure of living protoplasm is the 

 absence of homogeneous lattice regions, whereas the intrinsic struc- 

 ture of protoplasmic derivatives is as a rule conditioned by the ar- 

 rangement of the molecular elementary units in some lattice order. 



o 



This is due to the fact that protoplasm is made up of many varying 

 kinds of molecules (including specifically different polypeptides), 

 whereas the high-polymer constituent of a protoplasmic derivative 

 generally consists of one particular kind of macromolecules which 

 combine to form an orderly pattern with comparative ease and thus 

 lends itself to X-ray analysis. For this reason we are much better 

 informed on the submicroscopic structure of these mesoplasmatic, 

 metaplasmatic and alloplasmatic cell constituents than on the intrinsic 

 structure of the living substance. Thus, while we can only trace the 

 intrinsic structure of protoplasm in general outline, we have abundant 

 quantitative data concerning the ultrastructure of highly diiferentiated 

 cytoplasm, frame and reserve substances. This part of the monograph 

 will deal with those structures disclosed up to date and will be con- 

 cerned less with the physico-chemical than with the biological 

 questions inherent in the theory of microstructure. The macro- 

 molecular substances making up the bulk of the structures concerned 

 are mentioned within brackets after the sub-titles. 



§ I. Carbohydrates, Chitin and Cutin 



a. Meristen/atic Plant Cell Walls (Cellulose) 



The primary cell wall. There is a physiological and histochemical 

 difference between the primary cell wall of vegetable meristems and 

 the secondary membranes of fully grown tissues. It is mainly in their 

 surface growth that this difference stands out. the secondary wall 

 layers being, on the contrary, deposited by apposition against the ex- 

 panded primary wall during the corresponding growth of the mem- 

 brane in thickness. In many respects, therefore, the primary mem- 



