THE STEM AND 1T,S FUNCTIONS 



93 



other functions than support and {'oiuhiction. Many plants 

 have abandoned the erect habit, and their weak, slender stems 

 climb or scramble by various means over other objects or lie 

 prostrate on the ground. In certain herbs the main stem may 

 even become subterranean, in which condition it is known as a 



A B 



Fig. 44. — Summer (B) and winter (^4) eoiiditionof the same woody twig (Cherry). 

 The buds arise in the angle between leaf and steam. 



rooisiock or rhizome (Fig. 45). Typical stems give opportunity 

 for the storage of a certain amount of food reserves, especially 

 in pith and cortex, but in some species this function is so greatly 

 developed that the stem system, or certain parts of it, becomes 

 essentially a storage organ only. This condition exists in most 

 rootstocks, and its extreme development results in a reduction 

 of the stem to a short, thick tuber such as we know in the potato 

 (Fig. 46), which is morphologically a stem but now shows little 

 obvious resemblance to that organ. The bulb and the corm 

 (Fig. 47) are other examples of highly modified underground stems. 



