THE FLUID COMPONENTS OP PLANTS. 241 



soon as they enter the plant, they constitute its sap, 

 or common juice, to the nature of which, as one of 

 the general components of vegetables, we shall now 

 direct our attention. 



The motion of the sap, though constant during the 

 continuance of the life of the vegetable, isstill mostactive 

 in spring and midsummer, at which periods a much 

 greater quantity of fluid is found in the vessels of the 

 plant. The sap is in the same situation for the purposes 

 of the plant, as the chyle of animals is, while yet in the 

 thoracic duct, and before it is mingled with the blood, 

 and exposed in the lungs to be fitted for the purposes 

 of life. Neither is in a proper state for yielding the 

 various secretions, and adding, by the process of as- 

 similation, to the growth of the plant, or of the animal ; 

 but the analogy goes no farther. In the animal, the 

 digestive powers of the stomach and the action of the 

 mesenteric glands so change the food taken into it, 

 that no chemical analysis of the chyle produced from 

 it could lead to an accurate knowledge of the food, 

 which had been employed by the animal ; but in 

 plants, the food is already prepared in the ground be- 

 fore it is absorbed by the roots, and, therefore, were it 

 possible to obtain the sap from the vessels very near 

 to the extremities of the roots, we should be enabled 

 to discover, with considerable accuracy, the real food 

 of plants. This, however, cannot be accomplished ; 

 and as the sap, in its progress, dissolves some ready- 

 formed vegetable matter, which had been deposited 

 at the close of the preceding autumn, in the upper 

 part of the root and at the base of the stem, its origi- 

 nal properties are thus altered ; and the farther the 

 part, which is bored in order to procure the sap, is 

 from the root, the more vegetable matter this fluid is 

 found to contain. Were it possible to obtain the sap 

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