106 On the Anatomy of Vegetables; intended to substantiate 



the wood. How comes it then that the whole wood is stained with 

 the liquor, and in the root (where the spirals are stopped) doable 

 the (juantityof coloured woi>d is discovered ? If the spirals alone 

 received the sap, the wood should be coloured only where they 

 run; it would stop entirely in the root, and only half the wood 

 would be coloured. 



I have shown that the sap runs in wood vacancies instead of 

 sap-vessel'^, and how this reconciles the admirable observation 

 of Sir J. E. Smith concerning the splitting of the wood. Now 

 again, if the spirals carry the sap to the leaves, why put in re- 

 <]uisitiou the largest vessels in the tree to carry the sap on from 

 tlie leaves downward^s to the bark ? why such an increase of 

 vessels to convey the same quantity of liquid? — Surely there is a 

 contradiction here (see fig. 9). But the whole return of the sap 

 may be refuted by the simple truth, that a half pint cannot con- 

 tain a gallon. Mr. Knight supposes that all the quantity of sap, 

 which in mounting occupies ten times the size of the bark, in 

 descending again runs into the bark-vessels filled already with 

 their own liquid, yet does not increase their size. Thus a...a is the 



{/ark, and h b the wood. Z"^ is added to aa, and yet remains 



the same size ; nor in anv degree enlarges,or doubles its number of 

 vessels. Let itdescend ip.cversuch small quantities, it must all still 

 pass through the stem of the tree, which is infinitely too narrow 

 in its bark and too small to admit it; besides that it has but its 

 iinier bark vessels descending; all the others pass round tlie tree; 

 nor could I ever discover a vessel in the bark containing sap : 

 and there is certainly no confusing together two licjuids dif- 

 fering so much as the bark juice and sap. 



That famous trial which is always mentioned so triumphantly 

 as proving the descent of the sap, much better sliovvs the descent 

 of ifie bark juice. I mean cutting a gash in the tree, and its 

 increasing in the upper and not the lower orifice of the wound. 

 Now if the whole lump foruied is cut off and dissected, it is found 

 to be " a collection of coagulated bark juice, which of course 

 could not proceed downwards ; lumps of resin congealed, sap, 

 and half-rotten buds. The sap drawn there by the lymphatic 

 vessels, on account of the injury done by the cut, and the buds 

 drawn thereby the increase of nourishment*". How, if it had 

 been sap, it could be prevented running down, I cannot con- 

 ceive : but the bark juice coagulates in a moment, and the air 

 would soon accelerate this effect. But a more thorough proof 

 may still be given that there is no circulation of sap, by showing 

 that the vessels which Mr. Knight has chosen for the purpose are 

 muscles, and can therefore contain no sap ; and that the large 

 vessels are inner bark vessels. Innumerable authors, both 

 • See Phil. Mag. for Aug. 1815, p. 93. 



French 



