TYPES AND KINDS OF STEMS 



45 



the winter often " sprout," the sprouts or shoots developing from 

 the eyes. Sometimes when kept in a box or drawer, even in the 

 absence of light, they will form colorless shoots and a new crop 

 of small potatoes. If placed in a vessel in contact with a little 

 water, and kept in a warm room in strong light, green shoots and 

 leaves will develop, and many interesting experiments can be 

 performed with them.* 



77. The sweet potato is sometimes called a " root tuber." It 

 is not a true tuber since it is an enlargement of a root and not of 

 a stem. Sweet potatoes are propagated by planting the potato 



Fig. 46. 



Desert vegetation, Arizona, showing large succulent trunks of cactus with shrubs and 

 stunted trees. Open formation. (Photograph by Tuomey.) 



to obtain the young shoots, large numbers of which spring from 

 the fleshy root, not from true buds, but adventitious buds are 

 formed in the tissue of the root. 



78. Cacti. The cacti embrace a great variety in the form of 

 the stem. The stems are greatly specialized. They are succu- 



* See " Water Culture Method for Experimenting with Potatoes," Plant 

 World, n, 249-254, 1908. 



