MOTION OF THE SAP. 291 



wood, and the emiflion of roots, above, inftead of below, the Experiments 

 bate of the annual (hoots. The veflels of the bark (the taiftaux ll^znoStZi 

 propres of Du Hamel) commencing in the leaves, were formerly the fap in trees. 

 traced by M. Mariotte, and fubfeqnently by myfelf, (being 

 ignorant of his difcovery,) to the extremities of the roots ; and, 

 when a cutting or tree is planted in its natural pofition, the fap 

 paffes downwards through thefe, to afford matter for new roots, 

 and to increafe the bulk of thofe already formed, having given 

 proper nutriment to the branches and trunk in its defcent.- 

 But, in the inverted cutting, or tree, thefe veflels become in- 

 verted ; and, if their organization be fuch as I have fuppofed it, 

 a considerable part of that fluid, which naturally defcends, will 

 be carried upwards, and occafion the production of new wood, 

 above, inftead of below, the junction of the annual fhootwitli 

 the older wood, as in the experiments I have defcribed. The 

 force of gravitation will, however, ftill be felt ; and by its agency, 

 fuflicient matter to form new roots may be conveyed to thofe 

 parts of the inverted cutting, or tree, which are beneath the foil. 

 Befides, if we fuppofe a variation to exift in the powers or 

 organization of the veflels which carry the fap towards the 

 root, we may alfo attribute, in a great meafure, to this caufe, 

 the different forms which different fpecies or varieties of trees 

 aflume; for, if the fluid in thefe veflels be impelled with much 

 forc£ towards the roots, little matter will probably be depofited 

 in the branches, which, in confequence, will be (lender and 

 feeble, as in the vine ; and there is not any tree that has been 

 the fubject of my experiments, in which new wood accumulated 

 fo rapidly at the upper end of inverted plants. To an excefs of 

 this power, in the veflels of the bark, we may alfo afcribe the 

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

 power, the effects of gravitation will be, in a great degree, 

 fufpended; and the pendant branch will continue healthy and 

 ' vigorous, by retaining its due circulation. The perpendicular 

 branch will, however, ftill poflefs fome advantages; for in this, 

 gravitation will act on the fluid defcending from the leaves; 

 and thefe will of courfe abforb from the atmofphere with in- 

 creafed activity. A greater quantity of matter will therefore 

 enter, within any given portion of time, into veflels of the fame 

 capacity ; and this increafed quantity may frequently exceed 

 that which the veflels of the bark are immediately prepared to 

 carry away. Much new wood will in confequence be generated, 

 U 2 and 



