318 STATE POMOLOGICAL SOCIETY. 



was carefully measured by Prof. Graves and the senior class. The area of the 

 sections of the branches twenty feet from the ground was more than twice as 

 great as the area of a section of the trunk four feet from the earth, and the 

 proportion of sap-wood was of course much greater. 



AX IIS'TERESTIXG EXPERIMENT 



was undertaken in the Durfee Plant-house to determine how small a propor- 

 tion of sap-wood could conduct the necessary supply of sap to the foliage of a 

 growing tree, and also whether the bark alone could furnish the requisite water 

 to prevent the leaves from wilting. A specimen of Hibiscus S2ilendens, stand- 

 ing in the ground and having three stems from the same root, was selected for 

 trial. The shrub was growing rapidly, and was prepared for the experiment 

 as follows : Two of the stems were tied firmly to stakes, and the third left un- 

 disturbed. The first specimen had all the bark removed from one inch of the 

 stem, and then the wood was cut away till there remained only a small 

 piece of the outside layer of sap-wood, which was one inch long and seven- 

 sixteenths of an inch in circumference. This exposed surface was immediately 

 covered with grafting-wax to protect the tissues from the action of the air. 

 The amount of stem remaining was just one eighty-fourth of the original, 

 which was about four inches around. The healthy leaf-surface w^as fully 

 twenty-five hundred square inches, from both sides of which exhalation went 

 on to some extent, making five thousand square inches of exhaling surface. 

 The result was that the foliage remained perfectly fresh and vigorous for ten 

 days, until, on the tenth of November, the specimen was cut for the museum. 



THE OTHER STEM 



was used to determine whether by osmose, or in any other way, the crude sap 

 could ascend in the bark and supply the leaves with water. All the wood and 

 one-third of the bark were removed from a portion one-half inch in length, 

 the exposed tissues protected by wax, and the branches so pruned as to leave 

 only five hundred square inches of leaf-surface. The foliage all drooped in a 

 single hour and never recovered. This experiment showed that the bark was 

 altogether incompetent to furnish the requisite supply of crude sap to the 

 parts above it, although it was thick and succulent, and much greater in 

 quantity, when compared with the exhaling surface, than the piece of sap- 

 wood which showed such marvellous conducting power. If osmose were the 

 cause of the ascent of sap, it would seem that the abundant parenchyma 

 of the bark, intimately united as it is with the wood by the medullary rays, 

 must freely transmit the amount required in this case. But the leaves wilted 

 and perished as quickly as if the entire stem had been severed. 



A COUNTER MOVEMENT. 



Having thus demonstrated that crude sap ascends chiefly in the sap-wood of 

 exogenous trees, let us now consider a few facts which appear to prove that 

 there is a counter-movement of elaborated sap which is for the most part con- 

 fined to the bark. 



It is well known that if a narrow ring of bark be removed from the trunk 

 of a tree between the leaves and roots, then the deposition of wood ceases be- 

 low the girdled place, though above it the growth of the season ensuing will 

 be quite normal. This proves beyond dispute that the wood cannot convey 

 that portion of the elaborated sap which is essential to growth, and that it can 



