CHAPTER VI 



THE STRUCTURE AND FUNCTIONS OF STEMS, ROOTS, 

 AND LEAVES 



WOODY STEMS 

 GROSS STRUCTURE 



The most evident function of the stem is that of displaying 

 advantageously the leaves, flowers, and fruit for the performance 

 of their proper functions. The main stem is also an intermediary 

 between the roots and the leaves, and as such it performs impor- 

 tant functions in the storage of reserve foods and in the trans- 

 portation of water and soluble food materials. 



We shall soon learn that in its external features and in its 

 internal structure the stem is a living, active organ in which 

 structure and function are admirably correlated. In our study 

 of the woody stem we shall consider first its gross external 

 features and then its more minute internal structure. It may 

 interest the student to know also that woody stemmed plants 

 are now regarded by some botanists as the forerunners of the 

 soft-stemmed, herbaceous plants of the present day. It is there- 

 fore appropriate to reverse the usual order of presentation and 

 consider the woody stem first. 



External features. Fig. 45 represents the external features of 

 a shoot of a lilac which has been produced by a season's growth, 

 as described in the last chapter. In the specimen selected for 

 the illustration, both the main shoot and the smaller lateral 

 shoot have two lateral buds which have replaced the terminal 

 bud. This latter condition is the more common one in the lilac, 

 except in the sucker shoots which spring directly from the roots 

 of the old plants. In the figure it may be seen that the fallen 

 leaves have left definite scars, the leaf scars, below each lateral 



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