Circulating System of Plants. 143 



experiments. On the 17tli of January last, he exhibited 

 with a good microscope (in which too great a glare of light 

 was avoided, by interposing Varley's dark chamber,) several 

 specimens o^ Chm'ti previousli/ dissected ; and the motion of the 

 sap was demonstrated to the satisfaction of the then chairman, 

 Sir J. M'Gregor, and was seen by almost every one present. 



It is admitted that the visible motion of the sap has, by 

 recent observations, been verified only in three or four plants, 

 Chara, i^icus elastica, ^lisma Plantago, and perhaps Chelido- 

 nium : therefore, that the nature of the sap-vessels, in which it 

 generally moves, cannot, as yet, he determined. The course of 

 the sap in Chara is so far ascertained, that Mr. Burnett thinks 

 himself justified in declaring that each joint or limb has an 

 individual circidation ; and although it may have a communi- 

 cation with other joints, yet that its motion is complete in 

 itself. A section of a I'ootlet, or of a joint, shows it to con- 

 sist of two lateral, simple, semilunar ducts, each being the 

 channel of a current that traverses the root or joint in an 

 opposite direction to the other; the course of the one being 

 up, the other down. 



" These ducts, although not spiral in their structure, that is, 

 not spiral vessels, are spiral in their disjwsition ; being twisted 

 as it were round a central axis, and forming two separate 

 scalse, much in the same way as the wild worm is often scored 

 round the stems or branches of unfruitful trees." 



Having thus stated the exact and determinate extent of 

 this important observation, so vaguely and yet imposingly 

 announced in some of the public prints, it becomes a duty to 

 solicit the attention of those of your readers who do not see 

 the Philosophical or the Horticultural Transactions, to the 

 luminous hypothesis of Mr. Knight. It has ever been the 

 practice of that great man to keep no discovery concealed : 

 he has published what he has discovered, and that in a manner 

 which, as you. Sir, justly observe, in your JLncyclopcedia of 

 Gardenings " renders all the papers of this eminent horticul- 

 turist so truly valuable," namely, " by being accompanied 

 with a rationale of the practice." 



Wishing to obtain all the information within my power, I cor- 

 responded with Mr. Knight on the subject of the sap-vessels ; 

 particularly, as I was confident, as slated at p. 324. of the 

 Domestic Gardener' s Manual, that the late Sir J. E. Smith had 

 formed an erroneous opinion concerning Mr. Knight's view 

 of the office of the spiral vessels; and I was favoured in the 

 first instance with a reply, the substance of which I now add, 

 in order to furnish a concise idea of the hypothesis that re- 

 iterated and conclusive experiments have finally led him to 

 advocate. 



