200 



THAT S IT 



sels and ducts, 559, forming the 

 vertical system, and operating be- 

 tween the roots and leaves — the 

 whole being linked and connected 

 by cellular tissue, 1-543. 



The medullary rays, 5, radiating 

 from the centre, give a wedge- 

 iike appearance to the markings 

 of woods. Having a lighter colour 

 than the timber, they are called 

 the silver grain; and their pro- 

 portion and distribution gives 

 character to some of the favourite 

 woods used for furniture. 



The pith, 1, in young plants, 

 is filled with a nutritious fluid 

 containing grains of starch, and 

 is designed to nourish saplings 

 until they acquire a certain de- 

 gree of strength. The pith then 

 dies ; but though it disappears 

 from the older parts of trees, it 

 still prevails in the younger 

 shoots. 



The more immediate use of the 

 bark, 4, is that of giving pro- 

 tection to the wood. Without 

 the bark there could be no cam- 

 bium y or sap, and, therefore, 

 there could be no deposition of 

 woody fibre. It is also essential 

 to the life of the tree, from its 

 connection with the cellular sys- 

 tem, the medullary rays, and the 

 pith. It contains a large number 

 of vessels, 550, which convey air 

 and fluid ; and it is the receptacle 

 of secretions, such as tannin, 

 quinine, turpentine, &c. 



Endogenous * trunks are almost 

 peculiar to tropical climates. In 

 these plants the bundles of wood 

 sent down from the leaves do not 

 range themselves in layers on the 

 outer side of the previously formed 



wood, but pass down in irregulaf 

 masses near to the centre of the 

 stem. It is held, indeed, by 

 botanists, that the woody bundles 

 of an endogenous stem are a sort 

 of root emitted by the leaves, 

 plunging down into the cellular 

 substance of the stem. In the 

 pandanus, or screw pine, 7, these 

 bundles quit the sides of the tree 

 before reaching the earth, and 

 constitute aerial roots, 8. 



» Fr. m 



t vo Greek words, meaning to grow within. 



561. 



In endogenous stems the cellular 

 tissue bears a larger proportion to 

 the woody fibre than in the exo- 

 genous ; and the vessels are also 

 less numerous in proportion to 

 the cells. 



Endogenous plants are repre- 

 sented by palm trees, 9, with 

 their wonderful utility and 

 beauty ; but the class contains 

 plants of lesser growth, and a 

 large number of grasses. Endo- 

 genous trees are destitute of bark, 

 or have only a thin cuticle, which 

 is hard, dense, smooth, and 



