ASCENT OF THE SAP IN TREES. 85 



below my incisions, scarcely grew at all, whilst all the parts above the 

 incisions increased as rapidly as in the trees whose bark remained in the 

 natural state ; the upper lips of the wounds also made considerable 

 advances towards a union, but the lower ones made scarcely any. 



Soon after midsummer, those parts of the wood which had been 

 deprived of bark became dry and lifeless, to some depth ; and the sap, in 

 consequence, meeting obstruction in its ascent, some latent buds shot 

 forth, in some of the plants, below the incisions. When one of the shoots 

 which these buds produced was suffered to remain, the part of the stem 

 below it began immediately to increase in size ; but if it was at any dis- 

 tance below the incision above, the part between it and that incision still 

 remained very nearly stationary, so as to be, in the autumn, almost a 

 whole year's growth less than the stem above the incisions. 



Choosing other stocks, which had each a strong lateral branch, I 

 removed the bark, in the manner described, in two places ; the one above, 

 and the other below, each lateral branch. The sap here passed both my 

 incisions as freely as in the former experiment ; the lateral branches 

 between them grew with the greatest vigour, and the part of the stem 

 between those branches and the lower incisions increased much in size. 

 I varied these experiments in every way that occurred to me ; and the 

 result uniformly was, that those parts of the stems and branches which 

 were above the incisions, and had a communication with the leaves, 

 through the bark, increased rapidly ; whilst those below the incisions 

 scarcely grew at all, till a new communication with the leaves through 

 the bark was obtained, by means of a lateral shoot below the incisions. 

 It now appeared to me to be probable that the current of sap which adds 

 the annual layer of wood to the stem must descend through the bark, 

 from the young branches and leaves ; and to these my attention was in 

 consequence directed. 



Towards the end of the summer, when some young luxuriant shoots of 

 my apple-trees had attained a proper degree of firmness, I made four 

 circular incisions through the bark of each, as in the preceding instances ; 

 and I removed the bark in two places, leaving a leaf between the places 

 where the bark was taken off. Examining them frequently during the 

 autumn, I found that the insulated leaf acted just as the lateral branch 

 had done ; the part of the bark and stem between it and the lower 

 incision being apparently as well fed as any other part of the tree ; and 

 it grew as much. Making similar incisions on other branches of the same 

 age, I left similar portions of insulated bark, without a leaf between the 

 incisions ; but in these no apparent increase in the size of the wood was 

 discoverable. 



