THE CELL-MEMBRANE. 359 



by a prolonged soaking in cold alkaline solutions, or in 

 Schweizer's reagent ; by this treatment double pectates 

 which are soluble and gelatinisable are formed. 



The pectic body which exists in the thickness of the 

 wall survives this dissociating treatment and is probably the 

 pectose of Fremy. What are the relationships between it 

 and the cellulose have not yet been determined, but there is 

 a very intimate association between the two, and this pro- 

 bably a mechanical one, as they can be separated, but only 

 by methods which materially alter if they do not destroy 

 one or both. Mangin's mode of preparation of it has been 

 already described. 



The pectose and calcic pectate are thus found to be both 

 present in soft delicate tissues, but in different proportions. 

 In the young cells of meristems there is but little calcic pec- 

 tate, while pectose is in larger proportion. It is not certain 

 that in these cells it is mechanically combined with or em- 

 bedded in a cellulose matrix ; it may be united more closely 

 with it, forming a compound comparable to a glucoside 

 which splits up under the action of an acid, yielding cellu- 

 lose and pectic acid. 



In older cells, among which intercellular spaces or pas- 

 sages have appeared, the proportion of calcic pectate is 

 more prominent, though even in the younger ones the 

 limiting layer is composed of this substance. This outer- 

 most layer is quite free from cellulose. The calcic pectate 

 often collects over the surfaces of the intercellular spaces, 

 being, in fact, a continuation of the middle lamella of the 

 wall which has split in the formation of the passage. It is 

 easy to see also how the small plugs or concretions which 

 are often found in such spaces may be formed of the same 

 material. 



Though these two bodies are the forms of pectic com- 

 pounds which are most widespread, many intermediate 

 modifications are met with which present their own peculi- 

 arities with respect to solubility, afiinity for bases, etc. 

 Thus the pectates which form the middle lamella are some- 

 times gelatinisable, swelling up in water. Such a variety is 

 found between the cells of the lacunar parenchyma of Calla 



