GUMS, PECTINS, AND CELLULOSES 71 



The pectins more nearly approach to the composition, proper- 

 ties, and functions of the celluloses than do any of the other groups 

 of organic compounds. They have been extensively studied in 

 connection with the parasitism of certain fungous diseases which 

 cause the soft rots of fruits and vegetables. These parasites 

 usually penetrate the tissues of the host plant by dissolving out 

 the middle lamella material, which may sometimes serve as food 

 material for the fungus; but more often the parasite secures its 

 food supply from the protoplasm of the cell contents. In such 

 cases, the parasite secretes both a pectose-dissolving enzyme, 

 known as " pectase " and a " cellulase " which attacks the cell- 

 wall material in order to provide for the entry of the fungus into 

 the cells. Other enzymes, known as " pectinases," which coagu- 

 late the soluble pectins or pectic acids into insoluble jellies in the 

 tissues of the plants seem to aid the plant in resisting the pene- 

 tration by the parasite. 



CELLULOSES 



Used in its general sense, this term includes all those substances 

 which are elaborated by protoplasm to constitute the cell-wall 

 material. Cellulose proper is a definite chemical compound, whose 

 properties are well established. In plants, however, this true 

 cellulose is nearly always contaminated by various encrusting 

 materials; and in the process of wood-formation, the cell-wall 

 material continually thickens by the conversion of the cellulose 

 into ligno-cellulose and the protoplasm of the cell as continuously 

 diminishes in volume. Thus the protoplasm of the cell produces a 

 number of different kinds of material which are deposited in the 

 walls of the cell. All of these, taken together, constitute the 

 general group known as the celluloses. 



These may be divided into three classes: namely, (1) the hemi- 

 celluloses, (2) the normal celluloses, and (3) the compound cellu- 

 loses. 



The hemi-celluloses (pseudo-, or reserve celluloses) include a 

 series of complex polysaccharides which occur in. the cell- walls 

 of the seeds of various plants. They are found in the shells of 

 nuts, rinds of cocoanuts, shells of stony fruits, etc., and in the seed- 

 coats of beans, peas and other legumes. They are much more 

 easily hydrolyzed than the other members of this group, and when 



