TYPES OF STEMS. 



373 



i 



amount of food to supply the aerial stem for the development 

 of flower and seed. There are roots, however, from the bulb 

 and these acquire water for the aerial shoot, and when planted 

 in soil additional food is obtained by them. 



725. Corm. A corm is a thick, short, fleshy, underground 

 stem. A good example 



is found in the jack-in-the- 

 pulpit (Arisaema). 



726. Tubers. These 

 are thickened portions of 

 the subterranean stems. 

 The most generally known 

 example is the potato 

 tuber ("Irish" potato, not 

 the sweet potato, which 

 is a root) . The ' ' eyes ' ' of 

 the potato are buds on the 

 stem from which the aerial 

 shoots arise when the po- 

 tato sprouts. The potato 

 tuber is largely composed 

 of starch which is used for 

 food by the young sprouts. 



726a. Phylloclades. 

 These are trees, shrubs, or 

 herbs in which the leaves are reduced to mere bracts and stems, 

 are not only green and function as leaves, but some or all of the 

 branches are flattened and resemble leaves in form as in Phyl- 

 lanthus, Ruscus, Semele, Asparagus, etc. The flowers are borne 

 directly on these flattened axes. The prickly pear cactus 

 (Opuntia) is also a phylloclade. Examples of phylloclades are 

 often to be found in greenhouses. 



727. Undifferentiated stems are found in such plants as the 

 duckweed, or duckmeat (Lemna, Wolfna, etc. See Chapter III). 



Fig. 426. 

 Corm of Jack-in-the-pulpit. 



