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tiu; root cannot be supplied with air, and so the whole 

 perishes. Leaves b:)iug so necessary to all perennial 

 plants, a reversionary stock of them is provided. The 

 loaves of theje plants are always formed in autumn, 

 though not unfolded till (lie following spring: they 

 then open and increase in proportion to the motion of 

 the sap, and the quantity of nourishment the plant re- 

 ceives : these leaves also, though not yet appearing 

 out of the bud, may suffice for the extremely small mo- 

 tion which the sap of those perennial plants that drop 

 their leaves has in winter. 



But besides these autumnal leaves, there is another 

 set formed in spring and expanding till "midsummer. 

 These are of infinite service to many sort of trees, par- 

 ticularly to the Mulberry, as they save its life, when 

 the first set of leaves have been all eaten by the silk- 

 worms. 



The analogy between the parts of plants and those 

 of animals, may now more fully appear. The parts 

 of plants are 1. The root, composed of absorbent 

 vessels, analogous to the lacteals in animals ; indeed 

 performing the office of all those parts of the abdomen, 

 tnat minister to nutrition. 2. The wood, composed f 

 Capillary tubes running parallel from the roots, although 

 the apertures of them are commonly too minute to be 

 seen : through these, which are analogous to arteries, 

 the sap ascends from the root to the top. 3. Those 

 larger resiels, which are analogous to veins : through 

 tn< >e it descends from the 'top to the root. 4. The 

 bark, which communicates with the pith by little 

 strings, passing between th-;; arteries. 5. Tne pith, 

 consisting ol transparent globules, like the bubbles 

 thai compose froth. 



The sap enters the plant in the form of pure water, 

 and the nearer fie root the more it retains of that na 

 lure. Tne f uther it g >es, the more it partakes of the 

 n-miie of the plant : in the trunk and branches it re- 

 mains acid; in the buds it is more concocted, It is 

 fa'-th-tT prepared in the leaves, (as blood in the lungs) 

 which being exposed to the alternate action of heat by 

 H 4 



