CHAP, i The Cell 



191 



its cell walls. They are conspicuously present in paren- 

 chyma, collenchyma, bast, and meristem tissues, pectic 

 acid and pectose being the compounds of most general 

 occurrence. He confirmed an old statement of Payen's, that 

 the middle lamella or ' intercellular substance ' consists 

 almost entirely of calcic pectate. 



Mangin did not determine the relations between the 

 pectose and the cellulose of the wall, but claimed that 

 there is a very intimate association, probably of a mechani- 

 cal character, as they can be separated, but only by methods 

 which materially alter one or the other of them. 



The formation of the cell wall after the karyokinetic 

 division of the nucleus was described by Strasburger in 

 1882. He held that a transformation of the microsomata 

 or granules of protoplasmic nature into cellulose takes 

 place immediately after their formation into a plate across 

 the centre of the spindle. This view was clearly only 

 a tentative one, for it did not take into account the pheno- 

 mena of the separation of the cells of tissues under the 

 action of reagents. The method of maceration in strong 

 oxidizing liquids associated with the name of E. Schulze is 

 applicable to the very young cells of growing points as 

 well as to the older tissues. Mangin held that there is first 

 formed a layer of pectates, upon the surfaces of which 

 laminae of a mixture of cellulosic and pectosic substances 

 are laid down. On this view Strasburger's microsomata 

 are not protoplasmic but pectosic. The view of their 

 protoplasmic nature was based upon their staining yellow 

 instead of blue with chlor-zinc-iod, a reaction which, how- 

 ever, is consistent with Mangin 's suggestion of their com- 

 position. Mangin suggested, however, another hypothesis 

 to the effect that the wall, formed originally of cellulosic 

 and pectosic constituents, but known generally as cellulose, 

 undergoes at once on its formation differentiation into 

 three layers, of which the middle consists of soluble pectates. 



