UNDERGROUND STEMS 155 



has branches which look exactly like leaves. So far as 

 function is concerned they are leaves, but so far as origin 

 is concerned they are stems. If you examine this plant 

 cl6sely, you will notice that the apparent leaves grow from 

 the axils of small, scale-like structures. These small, scale- 

 like structures are the true leaves, while the leaf -like branches 

 which arise from them are exceptional forms of stems. Such 

 exceptional forms of stem branches are called cladophylls. 

 (The word means branch-leaf.) Asparagus 1 has already 

 been given as an example of a plant whose stems do work 

 ordinarily done by leaves. Its needle-Uke branches may 

 be also properly called cladophylls, though their resem- 

 blance to leaves is not so striking as in smilax. 



Thorns, as to origin, are sometimes stems, sometimes 

 leaves. The same is true of tendrils. Thus we note that 

 stems and leaves appear to be equally capable of becoming 

 the same organ as to function if not as to origin. The 

 honey-locust and the hawthorn are plants whose thorns 

 are stems as to origin. 



48. Underground St.ems. — Horizontally elongated un- 

 derground stems are called rhizomes or rootstocks. If a 

 portion at the end is much more swollen than the rest, it 

 is called a tuber. Underground stems sometimes bear 

 leaves. If the leaves are fleshy and arise from a short 

 stem, the structure thus formed is called a bulb. A bulb, 

 therefore, is an underground shoot, the word shoot, as you 

 know, denoting stem and leaves together. A corm is an- 

 other kind of underground shoot. In it the stem is more 

 prominent than the leaves, most of the food is stored in 

 the stem part, and the leaves may be simply protecting 

 scales. 



