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fluid is converted into a nutritious sap to assist the 

 development of new formations. Here in these 

 leaves, under the influence of the atmospheric air, 

 an incessant chemical change is going on, present- 

 ing very interesting phenomena which will be 

 discussed later on. But many observations have 

 yet to be made before we can fully understand the 

 mystical chemical processes by which the water of 

 the sap is decomposed, receives new elements, 

 assimilates them for the different functions of vege- 

 table life, and returns them eventually to the 

 cellular system of the stem, to be utilized in the 

 further development of the plant, or, if superfluous, 

 to be expelled through the medium of the roots. 



A superficial observation of a leaf will show that 

 the two sides are different in colour : the upper 

 side, which is generally glossy, seems to be a con- 

 tinuation of the epidermis of the stem, and serves 

 for the transmission of the light ; while the under 

 side, which presents a dull appearance, contains all 

 those little cells and tubes by which moisture is 

 evaporated or absorbed, and gases inhaled or ex- 

 haled, and which are called the stomata of the leaves. 



The processes of vegetation and the purposes of 

 the plant culminate in the production of the seed ; 

 and its importance as the propagator of new plants 

 is of course apparent. 



It has been mentioned before that the seed stands 

 in closer connection to the plant which is raised 



