FIBROVASCULAR TISSUES: RAYS 



only with one another, but often with the similar but larger secre- 

 tory cavities which are present in the bark. 



Fig. 50 illustrates the relation between the vertical and hori- 

 zontal resin canals as seen in a vertical section of the wood of the 

 Douglas fir (Pseudotsuga). To the left of the center lies a fusiform 

 ray with its included resin space, which opens broadly on the right 

 into a vertical secretory _____^ _ 

 canal. The plane of sec- 

 tion happens to lie near 

 the end of the annual ring 

 so that the cellular struc- 

 tures lying in view are 

 almost entirely parenchy- 

 matous. The lining of 

 the resiniferous spaces is 

 evidently largely com- 

 posed of elements with 

 thick walls and bordered 

 pits, a condition very com- 

 monly present in the 

 representatives of the 

 Pineae other than Pinus 

 itself. 



After the discussion of 



the pine and its nearer allies we may proceed with advantage to 

 the description of the ray structures in coniferous woods of simpler 

 organization. Fig. 51 illustrates the structure of the ray in the 

 wood of the balsam fir (Abies balsamea). It is clear that in this 

 case the cells of the rays are all of one kind and that the marginal 

 tracheids are conspicuous by their absence. The parenchymatous 

 elements which compose the rays in the genus under considera- 

 tion are in relation to one another on both vertical and hori- 

 zontal walls by numerous simple pits. The lateral walls show 

 bordered pores such as ordinarily, except in certain species of 

 Pinus, characterize the relation between rays and tracheids. 

 The organization of the linear rays in conifers other than the 

 Abietineae is in general of a simple nature; and in the higher 



FIG. 51. Ray of the balsam fir. Explana- 

 tion in the text. 



