TISSUES OF ANQI0SPERM8. 



447 



■bium cells by the formation of transverse partitions is very 

 clear in this figure. 



547. — In the trees and shrubs of cold climates, or of 

 those in which there is one annual period of growth, fol- 

 lowed by a period of rest or the cessation of growth, the 



Fis. 326. 



Pig. 327. 



Fig. 328. A tangential section of ttie cambinm region of Cytisus Laburnum, a, ft, 

 c, d, cambium cells enclosing the section of a medullary ray ; h, h, tracheides belong- 

 ing to the xylem. x 145.— After De Bary. 



Fig. 327.— Tangential section of the inner phloem regioii of the same stem as Fig. 

 326. 8, 8,8, sieve vessels ; m. section of a small medullary ray ; the remaining parts 

 of the figure are phloem parenchyma. X 145. — After De Bary. 



processes described above take place each year, giving rise, 

 thus to an annual layer of xylem (wood) outside of the pre- 

 viously formed xylem cylinder, and an annual layer of 

 phloem (bark) inside of the phloem cylinder. In the wood 

 these layers are generally quite well marked, and in cold 

 climates they enable us to determine with accuracy the age 



