316 ON THE CULTIVATION OF THE PERSIAN VARIETIES OF THE MELON. 



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 

 wonderful. He found, that under such circumstances water would pass 

 upwards through three folds of the substance of a recently-extracted 

 animal bladder, and in opposition to the perpendicular pressure of forty- 

 five inches of quicksilver ; which is nearly equivalent 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 it is through the cellular substance, and not through 

 the tubes of the alburnum, that the sap ascends, or its ascent would be 

 prevented, which it is not, by intersection of those tubes ; and those tubes 

 are also dry at midsummer, when the sap is rising to supply moisture to 

 the leaves in great abundance. Previously to the discoveries of M. 

 Dutrochet, I had shown that the sap of trees is lightest, or least dense, 

 near the ground ; and that in any particular tree, the weight of the sap 

 increases as its distance from the ground through the course of the albur- 

 num increases : and I had also proved that saccharine matter exists in 

 considerable quantity in the sap in the spring, in cases where no vestige 

 of it can be discovered in winter : and sugar was the material employed 

 by M. Dutrochet to form his denser fluid. These facts were not in any 

 degree known to M. Dutrochet when he made his discoveries, and he 

 therefore was certainly not led in any degree by me in making them. 



The sap in the leaves of my melon plants was certainly a denser fluid 

 than the water with which they were sprinkled ; and therefore I imagine 

 that the latter fluid passed in injurious excess into the cells and vessels, 

 and that the ingress and circulation of the proper fluid, which ought to 

 have continued to ascend from the roots, was to a great extent prevented, 

 and that the creation of the true or living sap of the plant almost wholly 

 ceased. The plant consequently, I conclude, ceased to grow, and the fruit 

 fell off, owing to want of proper nutriment. Soon after I had ceased to 

 sprinkle the under surfaces of the leaves, the young fruit began to set 

 well, and the plants to grow, but never with very great vigour ; and the 

 fruit, though its quality was exceedingly good, was smaller a good deal 

 than I conceived it would have been if the under sides of the leaves had 

 not been so frequently wetted. The weather was, however, very unfa- 

 vourable, and the fruit, I entertain no doubt, would have been larger, if 

 the foliage of these plants had received the benefit of more light. I have 



