THE STEM 



177 



two lateral traces of a leaf and may consequently be appropriately 

 called leaf or foliar rays. The less conspicuous rays in other radii of 

 the stem are in relation to other traces of other leaves lower or higher 

 in the stem. In the following illustration (Fig. 130) a portion of the 

 stem represented in Fig. 129 is shown. The greater magnification 

 makes it apparent that the broad radial band related to the out- 

 going leaf trace is in reality an aggregation of rays and not a simple 

 structure. It is, in 

 fact, largely com- 

 posed of fibers as 

 well as of radial 

 parenchyma, to 

 the exclusion of the 

 vessels which form 

 a prominent fea- 

 ture of the remain- 

 ing organization of 

 the wood. In the 

 case of the large 

 ray figured it is 

 clear that conspic- 

 uous depressions 

 mark the surface of 

 the annual ring 

 where the broad 

 radial band crosses 

 it. In Fig. 131 the same ray appears in the vertical section of the 

 wood. It is now evident that the structure in question consists 

 of an aggregation of rather small rays separated from one another 

 by fibers and including in their midst the transverse section 

 of a foliar strand or leaf trace. It will be obvious from the 

 various figures of the stem of the alder that in this genus there are 

 groupings of rays in relation to the foliar traces, and that these 

 storage bands on account of their topographical and physiological 

 relations may appropriately be designated foliar rays. 



It will now be convenient to refer to the conditions found in 

 the case of the oak. Fig. 132 illustrates a transverse section of 



FIG. 130. Part of transverse section of stem of Alnus 

 japonica, showing aggregate ray in relation to a leaf, more 

 highly magnified. 



