SHOOTS 



67 



cuiimiou trees may be known, even at a distance, liy tlieir 

 characteristic habits (see Figs. Od. lil. ni). The difficulty 

 of tlie mechanical problems solved l)v these huge bodies 

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

 dure tremendous i^ressure and strain. 



Fig. 5S. An elm iu its winter condition, stiowing the ab:^ence of a continuous central 

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

 On each side in the bacligruuud are trees of the pine type, showing the central 

 shaft and conical outline. 



