;- 



NATURE ' »!• O >RK TISSUE 



< inter daughter cell ad as the cambium cell while the inner cell 

 develops into one of the cells of the cortex. A.s soon as the 

 cork cells have reached their Growth, a substance called suber 



Fig. 40. Cross-section of the outer part of the stem of geranium. 

 The o>rk cambium, c, originating in the cells immediately In-low the 

 epidermis. 



begins to be deposited in their walls. This completely changes 

 the properties of the cellulose walls and renders them impervious 

 to fluids and gases. So the cork cells haw the same physical 

 properties as the cuticle of the epidermis and owing to the 

 continued activity of the cork cambium they are able to keep 

 pace with the growth of the stem. It is evident that the cork 

 cells must die as soon as they become impervious to fluids, and 

 it must also follow that all cells lying outside of these cork cells 

 will die since no fluids can reach them from the vascular bundles. 

 These dead cork cells give the characteristic aspect to the outer 

 hark of trees and we would naturally COme to think of the 



dark bark as composed of rather thick cells. As a rule, however, 



the cork cells arc quite delicate ami compactly put together 1 Im!4'. 

 \~ \ ami the dark color is more USUall) <\uv to tin- dried remain- 



- . 



Fig \j. 



Fig |8 



In,. 17 Us of bottle cork showing tin- delicate char* 



ells. 



Fig. 48 Scale bark of pitch pin< I nt-like lin«'- in 1 1 1 « - K.irk 



show tin itions "f the cork cambium. 



