Page:Proceedings of the Royal Society of London Vol 1.djvu/258

Rh strayed as soon as they became perceptible. An increased luxuriance of growth now took place in all the plants; numerous blossoms were emitted, and every blossom afforded fruit.

In another experiment Mr. Knight, taking great care to prevent the formation of tubers on any other part of the plant, permitted them to form on the extremities of the lateral branches; these being the points most distant from the earth, in which the tubers are naturally deposited. Many of the joints of the plants became enlarged; and our author thinks, that if the formation of tubers had been totally prevented, these joints would have acquired an organization capable of affording plants in the succeeding spring.

In another variety of the potatoe, which was very luxuriant in la- teral branches, Mr. Knight de ched many of those branches from the principal stem, letting them, however, remain suspended by such a. portion of albnmous and cortical ﬁbres and vessels as was suﬁicient to preserve life. The result was, that the true sap, instead of re- turning down the principal stem into the ground, remained, and formed small tubers at th'g. base of the leaves of the depending branches.

To ascertain whether the tubers would be fed when the passage of the true sap down the cortical vessels was interrupted, a portion of the bark, ﬁve lines in width, was removed from the stems of several potatoe plants, close to the surface of the ground, soon after the tubers had begun to be formed. The tubers continued to grow, but did not attain their natural size; partly, our author supposes, from the de- clining health of the plant, and partly from the stagnation of a por- tion of the true sap above the decorticated part.

The preceding experiments, Mr. Knight admits, do not prove that the ﬂuid contained in the leaf passes downward through the decor- ticated space to be subsequently discharged into the bark below it; but he has, he says, found that if the amputated branches of different trees have their leaves immersed in water, a portion of that ﬂuid will be absorbed, and will be carried downwards, by the albumnm, into the bark below a decorticated space; so that the insulated bark will be preserved alive and moist during several days. If the moisture absorbed by a leaf can be thus transferred, it appears very probable that the true sap will pass through the same channel. A considerable portion of that sap certainly stag-mates above the wound, and a great part of that which escapes into the bark below the wound, is pro- bably carried into the root. But some of that ﬂuid will be carried upwards, by capillary attraction, and will stagnate on the lower lip of the wound, where, inMr. Knight’s opinion, it generates the small portion of wood and bark described by Hales and Du Hamel.

Our author concludes his paper by stating, that he has in his possession a piece of a ﬁr—tree, from which a portion of bark, extending round its whole stem, had been taken off several years before the tree was felled. And he has ascertained that the speciﬁc gravity of the wood above the decorticated space is 0.590, that below it only 0.491 ; and having steeped pieces of each part, weighing 100 grains,