ORGANS. ROOT. STEM. 45 



by growing very rapidly through dough, in which its 

 seeds have been sown in the form of yeast, causes an 

 action which makes it swell and form light bread. Other 

 plants are formed of a single thickness of cells arranged 

 side by side and end to end. These also are usually 

 found growing in water. 



There are still others which consist of a few, often 

 only thrfio or six layers of cells, plants having length and 

 breadth with but little thickness. Such are the lichens 

 which form a thin crust on the bark of trees and on the 

 surface of rocks which have been long exposed to the 

 atmosphere. 



137. Most plants are formed of cells growing out of 

 each other in every direction, upwards, forming the stem, 

 downwards, forming the root, and on every side, forming 

 the thickness of root, stem and branches, and leaves and 

 flowers and fruits. 



138. The parts just enumerated, the parts of which the 

 plant is made up, are called the Organs. 



139. The principal organs are 1st, the root ; 2d, the 

 stem ; 3d, the leaves ; 4th, the flower ; 5th, the fruit. 



140. The Root is the part which penetrates from the 

 light into the earth, and gives the plant foothold, and the 

 means of obtaining nourishment. It usually divides into 

 smaller and smaller roots and rootlets, or radicles and 

 fibres, more and more slender, the cells along the sides 

 and extremity of which are the real mouths by which 

 most of the food of the plant enters into its circu 

 lation. The amount of food which a plant can receive 

 from the soil depends upon the number and surface of 

 the fibres of the roots. 



141. The Stem is the part of the plant which rises 

 upwards into the air and light, and supports the branches, 



