INTRODUCTION 55 



plant more easy to comprehend they are described 

 here. 



Of the non- nitrogenous substances the principal 

 are the carbohydrates, which are made up of carbon, 

 hydrogen, and oxygen. They include, in the first 

 place, sugars, which are usually dissolved in the cell- 

 sap. Of these the chief are glucose, dextrose, or 

 grape sugar, found in fruits such as the apple, which 

 contains up to 10 per cent, of these sugars. 



Fructose, fruit sugars, or levulose, also occur in 

 fruits, as the first two names indicate. Cane-sugar or 

 saccharose is found in stems and roots in the cell-sap — 

 in beet for example. This is the source of the sugar 

 now being derived from the beet industry in this 

 country. Maltose is another type found in grain. 

 An enzyme is the origin of fermentation in yeast. 

 Starch is found in the form of starch grains, in such 

 tubers as those of the potato. It occurs also in roots 

 and in grain or seeds generally. The grains differ in 

 form and size in different plants. Starch occurs in 

 two forms — granulose and farinose. 



Cellulose forms the basis of the cell-wall of plant 

 structures. Its occurrence in plants was at onetime 

 considered to be a distinction between animals and 

 plants, but it occurs also in animals. There are 

 different kinds of cellulose. Cellulose is found also 

 in lignified tissues. The celluloses are combined 

 with other compound celluloses, such as pectocellu- 

 loses, found in carrots, etc., adipocelluloses, found in 

 corky tissue as suberin, and in the cuticle as cutin, 



