CH. V] 



MEDULLARY RAYS. 



examined with a simple lens, two things will be apparent ; 

 the surface is longitudinally striped owing to the general 

 longitudinal character of the tissue, but there are also 

 very evident transverse markings. These must correspond 

 to radiating lines in the transverse section, and they are 

 in fact the medullary rays. In a section examined under 

 a higher power their structure comes out as shown in 

 fig. 32. 



X.J. X.9. 2C.3. 



FIG. 32. 



LONGITUDINAL KADIAL SECTION OF THE WOOD OF THE OAK. 

 a?j to # 4 represent the xylems of successive years, the dotted vessels 

 appear at the left of the brackets x 2 to # 4 ; at the left of x are the 

 spiral vessels of the protoxylem. 

 The medullary rays run like walls transversely across the section. 



Each medullary ray is like a wall of brick-shaped cells, 

 the bricks being supposed to stand on their edges ; their 



