290 History of the English Landed hiterest. 



lie had learned the true economy of vegetable life. He had 

 found that the first seed roots of corn die as soon as the o;her 

 roots above the grain come out near the surface. He had 

 measured the lengths of various farm plants, and he had a 

 very fair notion of the damage done by setting roots too low 

 or too high in the soil. Plants, he declared, had no stomach 

 like the animalia, and must therefore go and fetch food for 

 themselves instead of having it supplied like beasts and human 

 beings, Roots are the intestines of plants, and have their 

 mouths or lacteal vessels opening on their outer spongy super- 

 ficies. These take in food just like the animal lacteals by 

 means of pressure, and this motion is sustained by the increase 

 of their diameters in the earth. By the agency of the stalks 

 and leaves the vegetable economy discharges its superfluous 

 matter into the atmosphere. Air, he says, is most necessary 

 for the tree above ground to purify the sap by the leaves, as 

 the blood of animals is depurated by their lungs. Now 

 Bradley had alleged that air is part of the food of plants, 

 and here Tull's ideas were at variance. The latter was 

 accurate enough so long as he confined his remarks to roots. 

 He had enunciated an important truth when he suggested that 

 the office of the leaf is to discharge the superfluous matter into 

 the atmosphere ; but he would not concur with Bradley in 

 ascribing to the air a share in the materials ot vegetable food. 

 We know now that the green matter of the vegetable economy 

 in the presence of sunlight is capable of setting free the con- 

 stituents of the atmosphere, and that it can release the oxygen 

 while it retains the carbon of a gas, which might otherwise 

 render the air we breathe unsuitable for human health. 

 "Water and air were then, by Tull's showing, merely the 

 vehicles for conveying food into the vegetable economj^, while 

 the earth, under the influence of nitre and other salts, com- 

 prised the food itself. In this last respect the practical Tull 

 was, speaking generally, in accord with the theoretical Bradley. 

 The latter had said : " The Salts with which each Grain of 

 Corn is impregnated are not precisely destined for the Nour- 

 ishment of this numerous Race (plants). Their first Action 

 is to cut the covers that infold and wrap up the several 



