[Chap. VIIl 



THE TISSUE SYSTEM OF LEAVES 



69 



p> YOUNG LEAVES 



Fig. 32. Vertical section of the terminal bud of a coleus plant. Compare it with 



Fig. 31. 



primordium are completely filled with protoplasm and become stratified 

 in several (5-8) layers. As this protuberance expands farther — becoming 

 more leaf-like, but still very small — cells in the middle layers divide 

 irregularly and form groups of cells from which the vascular tissues of 

 veins develop (Fig. 33). 



In the leaves of many of our trees, to which the above description 

 particularly applies, this entire development proceeds slowly through 

 the spring, summer, and autumn months within the buds. By the end of 



