STRUCTURE.] 



THE SUBTERRANEAN STEM. 



179 



2. Of its External Modifications. 



It has already been stated, that the first direction taken by 

 the stem immediately upon its development is upwards into 

 the air. While, this ascending tendency is by many plants 

 maintained during the whole period of their existence, by 

 others it is departed from at an early age, and a horizontal 

 course is taken instead; while also direct communication 

 with light and air is essential to most stems, others remain 

 during all their lives buried under ground, and shun rather 

 than seek the light. From these and other causes, the stems 

 of plants assume a number of different states, to which 

 botanists attach particular terms. It seems most convenient 

 to divide the subject into the varieties of 



1 . The subterranean stem ; and 



2. The aerial stem. 



The SUBTERRANEAN stem was confounded by all the older 

 botanists, as it still is by the vulgar, with the root, to which 

 it bears an external resemblance, but from which it is posi- 

 tively distinguished both by its ascending origin, and by its 

 anatomical structure. (See Root.) 



2.5 



The following are the varieties which have been distin- 

 guished : 



N 2 



