7 6 



THE ANATOMY OF WOODY PLANTS 



allocated to particular and highly differentiated categories of cells. 

 In the present connection we are concerned only with the struc- 

 tures included under the heading of radial parenchyma. Clearly 

 the rays in the oak are of two types, even as seen in transverse 

 section. A small number are very broad and constitute a large 

 bulk of storage tissue. In contrast to these in respect both to size 

 and to number are linear rays, abundantly present in the figure. 



It is best in this 

 instance to focus 

 our attention on 

 the composition of 

 the uniseriate or 

 linear rays and 

 their relation to 

 the various ele- 

 ments represented 

 in the complex 

 organization of the 

 wood in the same 

 genus, Quercus. 



Fig. 57 repre- 

 sents the uniseriate 

 rays in radial and 

 tangential aspect. 

 In a is seen the 

 tangential view. 

 The ray is obviously composed of cells which are all alike and 

 related to one another and to the air spaces by simple pits. Half- 

 bordered pits connect ray cells with tracheids. In b and c are 

 shown radial aspects of the ray in relation to the various structural 

 elements of the wood. On the left and right in b files of vertical 

 parenchyma cross its course and are related to the radial elements 

 by groups of clustered pits. To the left of the middle of b is shown 

 a vessel (this type of element will be considered in the following 

 chapter) which communicates with the radial storage elements by 

 large, generally oval, pits. The rest of the width of b is occupied 

 by tracheids, which in turn communicate with the cells of the 



FIG. 56. Transverse section of the wood of the 

 red oak. 



