372 



RELATION TO ENVIRONMENT. 



not necessary since flowers are not formed. The mandrake, 

 Solomon's seal, Trillium, etc., have scale leaves on the fleshy 

 underground stems, while foliage leaves are formed on the aerial 

 stems, the latter also bearing the flowers. Some of the advan- 

 tages of the rhizomes are protection from injury, food storage 

 for the rapid development of the aerial shoot, and propagation. 



Many of the grasses have subterranean stems which ramify 

 for great distances and form a dense turf. For the display of 

 foliage and for flower and seed production, aerial shoots are 

 developed from these lateral upright branches. 



III. Specialized Shoots and Shoots for Storage of 

 Food.* 



724. The bulb. The bulb is in the form of a bud, but the 

 scale leaves are large, thick, and fleshy, and contain stored in 



them food products manu- 

 factured in the green aerial 

 leaves and transported to the 

 underground bases of the 

 leaves. Or when the bulb is 

 aerial in its formation, it is 

 developed as a short branch of 

 the aerial stem from which 

 the reserve food material is 

 transported. Examples are 

 found in many lilies, as Easter 

 Fig. 425. lily, Chinese lilies, onion, tulip, 



Bulb of hyacinth. ^ The ^^ ^^ ^^ ^ 



closely overlapped and surround the short stem within (also 

 called a tunicated stem). In many lilies there is a sufficient 



* Besides these specialized shoots for the storage of food, food-substances 

 are stored in ordinary shoots. For example, in the trunks of many trees 

 starch is stored. With the approach of cold weather the starch is con- 

 verted into oil, in the spring it is converted into starch again, and later as the 

 buds begin to grow the starch is converted into glucose to be used for food 

 In many other trees, on the other hand, the starch changes to sugar on the 

 approach of winter. 



