182 



THE ANATOMY OF WOODY PLANTS 



compound. In Fig. 136 the longitudinal view of the root in the red 

 oak is shown. It is now more than ever evident that the compound 

 condition of the rays characteristic of the stem of the oak, at least 

 so far as the red oak is typical of the genus, is not present in the roots, 

 but that in the latter organ the broad bands of radial storage 

 elements belong to the type denned as aggregate. In the case 

 of the root, in fact, one finds for many years of development that 



the more prominent 

 radial structures are 

 aggregate, a condi- 

 tion which gives 

 place in old and 

 thick axes to the 

 compound type of 

 organization. In 

 the seedling stem 

 or in branches de- 

 rived as the result 

 of injuries from the 

 lowest region of the 

 main trunk, the 

 aggregate ray occurs 

 and persists often 

 for a long period. In 

 anticipation of cer- 

 tain general prin- 

 ciples of comparative anatomy to be set forth in detail in a later 

 chapter of this work it may be stated that it is apparent in the 

 case of the oak that the aggregate condition of the rays has 

 preceded that defined as compound, and, in fact, that the aggre- 

 gate condition is the forerunner of the compound ray. It is 

 accordingly clear that as regards both the nature of the large 

 rays and the relationship which they bear to the appendages the 

 alder and the oak are substantially in a similar condition. In 

 other words, the question of large storage rays is one susceptible 

 of elucidation in accordance with well-defined evolutionary and 

 physiological principles. 



FIG. 135. Transverse section of large ray in stem of 

 Quercus rubra. 



