3i6 TEXTBOOK OF BOTANY 



more largely used in making sirup), and from the sap of the 



hard maple. Dextrose, otherwise known as glucose or grape 



sugar, occurs in grapes and many other fruits, and in honey. 



In nature it is usually associated with levulose (a sugar very 



similar to dextrose) and sometimes also with cane sugar. 



Dextrose is made commercially on a large scale by treating 



starch with sulphuric acid. It is only about three-fifths as 



sweet as cane sugar, and is correspondingly less valuable. 



It is largely used in brewing and in the making of sirups and 



candies. 



335. Foods for Animals. — Besides the cereal grains, which 



are relatively as important for domestic animals as they are 



for man, there are many forage plants — 



that is, those which animals eat, either 



fresh as they are growing, or dried in 



the form of hay. The most extensively 



used forage plants are various grasses, 



some of them wild and some cultivated. 



Some of the sedge family are also useful 



in the same way, being commonly known 



also as "grasses." In addition, certain 



„ ' ' ' , . members of the pulse family are very 

 Fig. 174. — The cnm- . f j j 



son clover. important forage plants ; their value for 



this purpose is due in large part to their 

 ability to use the free nitrogen of the air v.-ith the help of 

 the bacteria that live in their roots. It is for this reason 

 that the clovers, alfalfa, the cow pea, and the soy bean 

 can be raised successfully on nitrogen-poor soils and are 

 valuable, especially if the crop is plowed under, in increas- 

 ing the proportion of nitrogen-containing substances in the 

 soil. Of several clovers used as forage plants, the most widely 

 cultivated, especially in the northern United States, is the 

 red clover. Crimson clover, a species of European origin, 

 is raised to a considerable extent in the southeastern United 

 States. Alfalfa has long been grown in Europe, and more 



