254 Plant Physiology 



material) may be a factor in the apparent tendency to- 

 ward biennial fruit production, that is, to a greater 

 production in alternate years. It stands to reason 

 that a too heavy yield of fruit one season may have 

 some effect upon the crop of the next year, although 

 this tendency may be offset to a considerable extent by 

 good culture, fertilization, and favorable season. 



142. Carbohydrates. - The carbohydrates include the 

 sugars, starch, cellulose, and many of the other compounds 

 containing carbon, hydrogen, and oxygen. They consti- 

 tute the bulk of food-materials in general. In these sub- 

 stances the molecule contains hydrogen and oxygen in 

 the proportion of 2 : 1 , or as in water ; and the number 

 of carbon atoms is usually six or a multiple of six, but in 

 some compounds five. The following are some important 

 classes of these compounds : - 



(1) Monosaccharids (sugars), C 6 H 12 6 , including glu- 

 cose, fructose, and galactose. 



(2) Disaccharids (sugars), C^H^On, including sucrose 

 (cane sugar), lactose (milk sugar), and maltose. 



(3) Polysaccharids or amyloses, n (C 6 H 10 O 5 ), including 

 such compounds as starch, inulin, dextrin, glycogen, and 

 cellulose. 



Briefly stated, the disaccharids and polysaccharids are 

 for the most part readily convertible into monosaccharids 

 through hydrolysis. This may be accomplished by boil- 

 ing with acids, and also through the action of certain other 

 compounds of metabolism, the enzymes, subsequently 

 discussed. The transformation of cane-sugar may be 

 represented as follows : - 



C 12 H 2 2O n -|- H 2 O = C 6 H 12 O 6 -|- C 6 H 12 O 6 , 



