S4 



ORIGIN OF LEAVES AND BRANCHES 



deeply located cells in the cortex co-operate in their formation. 

 This relationship of the leaves and branches to the stem is shown 

 in Fig. <>_>. which is a diagram of an elongating stem, showing the 



relation of the apical region of the stem ( </ in Fig. M (, to the 

 lower and older portion. The cells in these young leaves ami 

 branches by rapid division and growth SOOn form the character- 

 istic ti^ne- already noted in the Leaves and stems: while a cor- 



Fig. 63. Section through the trunk of basswood showing relation of 

 branches to main stem. In the upper portion of the figure arc three 

 branches thai were killed after a few years' growth by shading and that 

 have been overgrown by the annual rings of the wood. The branch shown 

 at a has remained alive and increased in size after the manner of the 

 main stem. 



responding growth in the cortex and adjacent regions results in 

 the formation of vascular bundles tli.it connect the vascular 



bundles of the stem with those of the leaves and branches. When 

 a leaf falls off, tin- ends of these vascular bundles can be easily 

 seen in the leaf -ear 1 Fig. 28, A 1 but owing to their minuteness 



it is not an easy matter to trace them through the stem to the 

 point where the\ join OH to the bundles of the stem. In the 



branch, however, owing to its size and wood) character, the 



union with the stem is V er\ manifest. Fig. 63 shows several 



small branches thai continued to keep pace for one or more 

 with the growth of the stem, bu1 eventually they were 

 killed by tin- overhanging branches and in time became over- 

 grown with the annual layers of xylem. If the branch i- favor- 



