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stroyed 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 detached many of those branches from 

 the principal stem, letting them, however, remain suspended by such 

 a portion of alburnous and cortical fibres and vessels as was sufficient 

 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 tile 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 alburnum, 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 stagnates 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, in Mr. 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 pos- 

 session 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, 



