MODIFIED STEMS 51 



case of trailers the plant is enabled to secure a large light 

 exposure by spreading over a large surface of ground. The 

 stem, in this case also, serving only the function of conduction. 

 Climbers from their habit are adapted to forested regions, 

 while trailers flourish in open ground. 



109. In many cases trailing stems take root at the nodes. 

 Such stems are called runners, or stolons. The object of such 

 a habit may be simply supplementary to the function of the 

 basal root system or else, if the stem also produces a system 

 of branches at the nodes, it may result in the production of 

 new plants an asexual method of reproduction. In this case, 

 after the young plant has become firmly established the stolon 

 connecting it with the parent may die, leaving the young plant 

 independent. If the connecting stolons persist it is possible 

 that the associated individuals may be of mutual physiological 

 assistance at critical times in the way of furnishing each other 

 nourishment, etc. It is certainly true that such plants growing 

 on a shifting soil are of great mutual assistance in holding each 

 other in place and thereby also holding the soil. Stolons may 

 be either above or under the ground. 



no. Underground stolons are sometimes greatly enlarged 

 at the end, forming tubers. This is due to the accumulation of 

 food substances for the purpose of storage, which is one of the 

 normal functions of the stems of perennial plants. In the larger 

 perennials the normal stem is large enough to provide sufficient 

 storage and consequently no special enlargement is necessary. 

 In the case of the smaller herbaceous perennials, however, there 

 is insufficient storage room provided by the comparatively 

 small normal stem and therefore the storage stems are enlarged. 

 Moreover, since the normal herbaceous stems usually do not 

 survive the winter, the stems which are modified for storage are 

 developed underground, where they are protected, and whence 

 they put forth shoots in the following spring from terminal 

 and axillary buds. 



