I * &amp;lt; 



CHAPTER V. 



FORMATION OF PLANTS. 



146. It lias been already stated that plants are formed of or 

 ganic and inorganic elements, which they receive from the soil 

 and air. (See 81-93.) The living plant possesses the power 

 of receiving into itself these bodies, of changing or digesting 

 them, and of re-arranging them in a different way, so as to pro 

 duce new substances. In the same manner a new born animal 

 swallows milk, and changes the milk into blood, bones, muscles, 

 brain, &c. The perfect tree is only air, water, and a portion of 

 the soil in which it is growing ; as the animal, a few months 

 old, is only milk in a different shape. If the soil does not con 

 tain all the materials requisite to form a plant&amp;gt; it either will not 

 grow at all, or it will grow unhealthily. 



147. A perfect plant consists of three parts, (a,) a root, which 

 remains in the soil, (b,) a trunk or stem which branches into 

 the air, and (c,) leaves. Each of these is differently formed, 

 generally contains different proportions of the elements, and is 

 endowed with a peculiar function. 



148. The stems of plants differ in their construction, some 

 being much more simple than others. The stem of a tree con 

 sists of three parts : (a,) the pith, in the centre ; (b,) the wood 

 surrounding the pith ; and (c,) the barks which cover the whole. 

 The pith consists of soft celular tissue (or parenchyma,) which 

 is at first gorged with the nourishing juices of the plant, but 



