170 LEAVES FROM THE BOOK OF NATURE. 



season, we speak of it as an herb, while a shrub has al- 

 ready a greater size and a stem that branches at the base. 

 The tree lifts its head high into the air, and divides mostly 

 above. The stems of climbers and creepers are long, thin 

 and winding, whilst runners crawl along on the ground or 

 beneath it, and produce new plants at their termination. 



The stem has frequently a decided tendency to grow 

 spirally; in creepers it is twisted from the root to the 

 end, the better to enable them to lay hold of and to em- 

 brace the objects around which they twine. So it is in 

 all climbing plants and their tendrils, and they derive from 

 this peculiar structure such strength, that they are found, 

 in South America, to form long, slender, but perfectly 

 safe bridges over broad rivers. Even large trees have 

 frequently the same spiral tendency, as we see in many 

 a blasted trunk in our forests, or when we attempt to 

 remove the bark from a cherry tree, which will not tear 

 straight and must be torn off in a spiral. 



In the stem, also, we see the main differences of the 

 growth of various kinds of wood in a beautiful variety of 

 grain and wavy lines. Its outside is protected by bark, 

 sometimes smooth, as if polished ; in others, as in the 

 pine, carved in huge square pieces ; hard and invulner- 

 able as stone in the cypress, but cut and cracked in the 

 elm. Most mountain trees have their bark deeply fur- 

 rowed with numerous channels, to lead the moisture of 

 rain and dew down to the rocky home of their deep 

 buried roots. Dark colored and soft in tropic climes, to 

 resist the heat, it is white as snow in the Arctic regions, 

 and in northern trees, as birches and willows, in order 



