130 



A DISCOURSE 



1U)0K II. putrid, sour, acrimonious, vitriolic, arenous, and gravelly, churlish, harsh, 

 ^■'^'y^'^^ and lean (I mention tliem promiscuously) ; and whatever vicious quality 

 they are perceptibly tinctured and impregnated with, they are by no 

 means proper diink for plants. Wherefore, a very critical examen of this 

 so necessary an element (the very principle, as some think, and only 

 nutriment of vegetables) is highly to be regarded, together with more 



It is evident, however, that, as water contains but few particles that are fit for nourish- 

 ment, it was necessary that plants should have the power of imbibing a large portion of 

 that fluid. For which reason the sun-flower, considered bulk for bulk, takes in seventeen 

 times more nourishment than a man, and consequently perspires more. During the con- 

 tinuance of dry north-east winds, the leaves of corn are observed to grow yellow, and the 

 early-set fruit frequently falls off. This is owing to the want of moisture in the atmosphere 

 to fill the vessels of the leaves and top-branches, whereby the fruit is deprived of nouiish- 

 ment. Under such circumstances, it is probable that wall-fruit may be preserved by 

 prudently watering the leaves and top-branches during the decline of the day. It is, 

 however, a singular happiness that the air is, at no time, perfectly free from moisture.-— 

 Bring a bottle of cold water into the warmest room, and its surface will immediately be 

 covered with a thick dew. An air absolutely dry, would, in a few days, annihilate the 

 vegetable creation. The air is justly said to contain the life of vegetables, as well 

 as animals. It is a compressible and elastic fluid, surrounding the face of the globe, and 

 reaching to a considerable height above it. Vegetables do not grow in vacuo, and animals 

 die when deprived of air. It has two states, being either elastic or fixed. Dr. Hales 

 observes, that, in its elastic and active state, it conduces to the invigorating the juices 

 of vegetables ; and, in its fixed and inert state, gives union, weight, and firmness to all 

 natural bodies. By his experiments we are informed, that fixed air constitutes near one- 

 third part of the solid contents of the heart of Oak. It is found to bear the same propor- 

 tion in peas, beans, and other vegetable substances. Heat and fermentation render 

 it elastic. It is again capable of being absorbed and fixed. Was the whole air of the 

 universe brought at once into an elastic and repulsive state, every thing would suffer 

 a sudden dissolution. Was it entirely fixed, then all things would be reduced to an inert 

 lump. ' Almighty Providence has provided against these extremes, and, in the most 

 wonderful manner, preserves the balance. Air is to be found in every portion of earth ; 

 and as it always contains a solution of the volatile parts of animal and vegetable substances, 

 ■we should be careful to keep our stiff soils as open as possible to its influence. It passes, 

 both in its active and fixed state, into the absorbent vessels of the root, and, mixing with 

 the juices of the plant, circulates through every part. Dr. Hales, in his statical experi- 

 ments upon the Vine, discovered it ascending with the sap in the bleeding season. 



Having demonstrated that the motion of the sap depends upon the influence of the air, 

 and the power of absorption common to all capillary tubes, it naturally follows, that 

 it cannot remain one moment at rest. The gradations from heat to cold, and vice versa, 

 are infinite, and sometimes desultory. So must be the motion of the sap. From the 



