By Thomas Andrew Knight, Esq. 87 



and rather freely, with water. By these measures the increase 

 and spreading of the red spider, was effectually prevented; but 

 on my return from London, I found that my plants had wholly 

 ceased to grow, though their appearance was healthy; and sub- 

 sequently all the fruit dropped off either before or soon after their 

 blossom had expanded. I in consequence immediately ordered 

 other plants to be raised, still, however, entertaining hopes of pre- 

 serving those I had. But those hopes were not realized; and I 

 was obliged to throw away the whole of them, with the exception 

 of one, which was more healthy than the others, and which lived 

 to produce the first fruit sent to the Society. That appeared to 

 be, as it proved, of good quality ; but it was defective in size, its 

 weight seemed little, if any thing, more than five pounds. 



My second family of plants were treated nearly, as the first had 

 been, and with the same approaching results : but I was led by the 

 discoveries of M. Dutrochet to change my mode of management ; 

 and I believe, to discover the cause of the preceding failure. This 

 eminent physiologist had discovered that if a lighter fluid be in 

 contact with one side of an animal, or vegetable membrane, and a 

 denser fluid with the opposite side, the lighter fluid will rush into 

 the denser, through the membrane, though that be under other 

 circumstances impervious to it. The force with which the lighter 

 fluid, in some of the experiments of M. Dutrochet, rushed through 

 animal membranes into the denser, appears to be exceedingly won- 

 derful. He found, that under such circumstances water would 

 pass upwards through three folds of the substances of a recently 

 extracted animal bladder, and in opposition to the perpendicular 

 pressure of forty-five inches of quick-silver ; which is nearly equiva- 

 lent to a pressure of twenty-two and a half pounds upon a square 

 inch of surface. This power in vegetable membranes to transmit 

 the lighter into the denser fluid is, I think, probably in active 

 operation during the ascent of the sap of trees in the spring ; for 



