SHOOTS. 



67 



common trees may be known, even at a distance, by their 

 characteristic habits (see Figs. GO, 61, 62). The difficulty 

 of the mechanical problems solved by these huge bodies 

 is very great. They maintain form and position and en- 

 dure tremendous pressure and strain. 



Fig. 58. An elm in its winter condition, Bhowing the absence of a continuous central 

 shaft, the main stem soon breaking up into branches, and giving a spreading top. 

 On each side in tbe background are trees of the pine type, Bhowing the centra] 

 phaft and conical outline, 



