TISSUSS OF ANG10SPERM8. 



447 



bium cells by the formation of transverse partitions is very 

 clear in this figure. 



547. — 111 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 



Kq. 326. 



Fis. 327. 



Pig. 336. A tangential section of the cambium region of Oijtisus Labumwrn. a, &, 

 e d, cambium cells enclosing tbe section of a mi'dnllary ray ; A, /i, tracheides belong- 

 ing to the xylem. X 145.-AfterDeBavy. 



Pig. 327.— Tangential siction of the inner phloem region of the same stem as Fig. 

 326. 5, fi,5, sieve vessels' ; m. section of a small medullary ray ; Ihe remaining luirts 

 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 



