MOTION OF THE SAP IN TREES. 107 



below, the junction of the annual shoot with the older wood, as in the 

 experiments I have described. The force of gravitation will, however, 

 still be felt ; and, by its agency, sufficient matter to form new roots may 

 be conveyed to those parts of the inverted cutting, or tree, which are 

 beneath the soil. Besides, if we suppose a variation to exist in the 

 powers or organisation of the vessels which carry the sap towards the 

 root, we may also attribute, in a great measure, to this cause, the 

 different forms which different species or varieties of trees assume ; for, 

 if the fluid in these vessels be impelled with much force towards the 

 roots, little matter will probably be deposited in the branches ; which, 

 in consequence, will be slender and feeble, as in the vine ; and there is 

 not any tree that has been the subject of my experiments, in which new 

 wood accumulated so rapidly at the upper end of inverted plants. To 

 an excess of this power, in the vessels of the bark, we may also ascribe 

 the peculiar growth of what are called weeping trees ; for, by this power, 

 the effects of gravitation will be, in a great degree, suspended ; and the 

 pendent branch will continue healthy and vigorous, by retaining its due 

 circulation. The perpendicular branch will, however, still possess some 

 advantages ; for, in this, gravitation will act on the fluid descending from 

 the leaves ; and these will, of course, absorb from the atmosphere with 

 increased activity. A greater quantity of matter will therefore enter, 

 within any given portion of time, into vessels of the same capacity ; and 

 this increased quantity may frequently exceed that which the vessels of 

 the bark are immediately prepared to carry away. Much new wood will 

 in consequence be generated, and increased vigour given ; and, the same 

 causes operating through successive seasons, will give the ascendancy we 

 generally observe in the perpendicular branch. 



In the preceding experiments none of the layers, or cuttings, exceeded 

 a few inches in length ; and, to the summit of these the sap appeared to 

 rise, through the inverted tubes of the wood, nearly as well as in those 

 which retained their natural position. But some further experiments 

 had induced me to suspect that this would not be the case in longer 

 cuttings ; I therefore planted, in the autumn of 1802, twelve cuttings of 

 the sallow, (Salix caprea.) inverting one-half of them. The whole readily 

 emitted roots, and grew with luxuriance ; but their modes of growth 

 were extremely different. In the cuttings which stood in their natural 

 position, vegetation proceeded with most vigour at the points most 

 elevated ; but, in the inverted cuttings, it grew more and more languid 

 as it became distant from the ground, and nearly ceased, towards the 

 conclusion of the summer, at the height of four feet. The new wood 



