CHAPTER VII 

 METAPLASM ; POLARITY 



In the foregoing chapters we have described successively the various 

 organs of the cell. Our account of the resting cell will now be com- 

 pleted by passing in brief review some of its more conspicuous non- 

 protoplasmic inclusions. We shall also call attention to another 

 characteristic but imperfectly understood attribute of the protoplast, 

 namely, its polarity. 



Metaplasm. — In addition to their definite cell organs— nucleus, 

 cytoplasm, centrosomes, plastids, and possibly chondriosomes -cells 

 which have undergone any amount of differentiation usually contain a 

 variety of other materials representing products of metabolism. Many 

 of these substances are held in solution in the cell sap, itself a differentia- 

 tion product, while others are present in insoluble form in the cytoplasm, 

 often in special vacuoles. All such non-protoplasmic inclusions, partic- 

 ularly those existing in some visible form, are referred to as metaplasm, 

 a term introduced by Hanstein. Although it has been held by sonic 

 (Kassowitz 1899) that metaplasm is always inactive and to be sharply 

 set apart from active protoplasm, it is more probable, as Child (1915 

 contends, that no absolute distinction can be made between the two. 

 Most of the products of differentiation, however, are clearly non-proto- 

 plasmic and relatively inactive. 



In cells of many types, even in the comparatively undifferentiated 

 cells of the root meristem, there often occur accumulations of chemically 

 complex substances in the form of small globules or irregular masses in 

 the cytoplasm. In many cases these more or less transient bodies, which 

 often stain intensely with the nuclear dyes and arc therefore referred to 

 as "chromatic bodies," show reactions indicating a composition closely 

 approaching that of the extra-nuclear granules of uucleo-protein (chro- 

 midia) which R. Hertwig and Goldschmidt interprel as granules of escaped 

 chromatin concerned in cell differentiation. Others resemble the fatty 

 chondriosomes in form and composition. It is therefore a mat ter of some 

 difficulty to distinguish between these various substances, which, as a 

 matter of fact, probably do not represent sharply distinct classes. 



The most conspicuous non-protoplasmic inclusions represent food 

 materials in transitory form or in the storage condition; they are conse- 

 quently abundant in cells carrying a supply of reserve foods, such as 

 spores and eggs, and in storage organs, such as many roots and the endo- 



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