ASCENT OF THE SAP IN TREES. 89 



along the tubes of the alburnum, or along the central vessels, I had little 

 doubt that the fruit was fed through the latter ; but my efforts to ascer- 

 tain this, in the autumn of 1799, were not successful. In the last spring 

 I was more fortunate. Placing small branches of the apple, the pear, 

 and the vine, with blossoms not yet expanded, in a decoction of logwood, 

 I found that the colouring matter readily passed up the central tubes of 

 the fruit-stalks of all ; and in the apple and pear, I easily traced it, 

 through the future fruit, to the base of the stamina. The office of the 

 tubes in the bark did not appear in this experiment; but as I have 

 reason to believe the motion of the sap in the bark to be always retro- 

 grade, I am disposed to conclude that it is so here, and that, through the 

 bark of the stalk, any superfluous humours existing in the fruit, from 

 excessive humidity of weather, or other cause, are carried back, and 

 absorbed by the tree. I have, however, very frequently repeated an 

 experiment on the vine, which, I think, evidently proves that the fluid 

 returned (if any), is essentially different from that which is derived from 

 the leaf. In the culture of this fruit, I have frequently pinched off the 

 young shoot, immediately above a branch, as soon as the latter 

 became visible in the spring, letting the leaf opposite the bunch remain. 

 In this case, the wood below the upper leaf acquired nearly its proper 

 length and substance. But when I have taken off that leaf, the wood 

 between the bunch and the next leaf below, has ceased to elongate ; and 

 has remained, in form and substance, similar to the small fruit-stalk 

 attached to it. 



I was long at a loss to conjecture by what means nutrition was con- 

 veyed to the seeds of the apple and pear ; for I had reason to believe that 

 it was not done by the medulla ; and I had previously ascertained that 

 the seeds would derive nourishment from the pulp, when the fruit was 

 taken prematurely from the tree. At length, in a large apple, which was 

 just beginning to decay, I found a number of minute vessels, leading from 

 the pulp to the tubes which originally constituted the lower parts of the 

 pistilla, and to which the seeds are attached. These now appeared to 

 me evidently to be the channels of nutrition to the seeds ; and since I 

 have known what I have to look for, I find these vessels sufficiently visible 

 in every apple : there are, however, five other tubes, which pass alon^ 

 the external edges of the cells of the core, to which I do not venture to 

 assign an office. It appears to me not very improbable, that the internal 

 organization of this fruit will be found to bear some resemblance to the 

 placenta and umbilical cord of the animal economy. If transverse and 

 longitudinal sections of young apples and pears be made, soon after the 



