THE VEGETATIVE ORGANS OF PLANTS. 



271 



of the bast or inner bark of our common trees; those 

 nearest the centre of the stem, c, are icood-cells. In the 

 maize stem, bast and wood-cells are quite alike, and 

 are distinguished only by their position. In other plants, 

 they are often unlike as regards length, thickness, and pli 

 ability, though still, for the most part, similar in form. 

 Among the wood-cells we observe a number of ducts, d, 

 e,f, and between these and the bast-cells is a delicate and 

 transparent tissue, g, which is the cawbium in which all 

 the growth of the bundle goes on until it is complete. On 



H 



nun 



i 



Fig. 49. 



either hand is seen a remarkably large duct, #, #, while the 

 residue of the bundle is composed of long and rather 

 thick-walled wood-cells. 



Our understanding of these parts will be greatly aided 

 by a study of fig. 49, which represents a section made 

 vertically through the bundle from c to h, cutting the va 

 rious tissues and revealino- more of their structure. In this 



O 



the letters refer to the same parts as in the former cut : 

 , #, is the cell-tissue, enveloping the vascular bundle; 

 the cells are observed to be much longer than wide, but 

 are separated from each other at the ends as well as sides 



