234 Retrospective Criticism. 



of detecting the presence of magnesian limestone ; and a simple method of 

 ascertaining the value of maris. Mr. Stapleton brought forward a number of 

 substances which remained insoluble after an analysis of the ashes of the vine ; 

 he also showed the principle of capillary attraction with two panes of glass, 

 and small glass tubes. Mr. Ayres considered that Mr. Keane had paid too 

 much attention to the opinions of Sir Humphry Davy, as that eminent chemist 

 was in error in several points, more especially in his recommending the use of 

 fresh manure ; it being now known that mamire possesses the greatest fertilising 

 influence when used in a decomposed state, from the humic acid it contains. 

 Mr. Stapleton informed the Society that Mr. Layton, a chemical gentleman, 

 would be happy to give several lectures to the Society ; and the Society, having 

 passed a vote of thanks to Mr. Layton, commissioned Mr. Stapleton to state 

 that the Society would be obliged by his services. 



Art. V. Retrospective Criticism. 



Erratum.— In Vol. XII. p. 554. line 15., for " 30ft. high," read " 13 ft. 

 high.' ' 



Increase of the Stump of the Silver Fir, without the Aid of Leaves, (p. 142.) — 

 I feel not a little gratified, and certainly much obliged to you, for inserting M. 

 Dutrochet's account of the growth of the roots of the silver fir so long after 

 the tree had been felled. It is some confirmation, I think, of my own ideas 

 regarding the local developement of the vital membrane, and non-descent of 

 the sap, published some years ago. M. Dutrochet's endeavours to ascertain 

 the fact, in the first place, and his candour in afterwards publishing it, show 

 him to be a lover of truth ; because this fact not only contradicts some of his 

 own previously declared opinions, but those of many of his most intimate 

 friends and coadjutors in the investigation of vegetable economy and botanical 

 research. 



We have cause to regret that that eminent physiologist has not appended 

 his own explanation of this curious phenomenon to the naked fact ; as it is 

 probable he would have entered into a justification of the opinion of Du Hamel, 

 Knight, De Candolle, Lindley, &c., who have all affirmed, as ah indisputable 

 doctrine, that the accretion of the stems and roots of trees is accomplished by 

 the subsidence and organisable properties of the elaborated sap. This he 

 (M. Dutrochet) would very naturally have done, not only in his own behalf 

 and that of his friends, but for the sake of the science itself. It would be 

 curious, too, to see how he would apply his own favourite doctrine of the 

 exosmose and endosmose currents of the sap in vascular tissue, where no cir- 

 culation of the fluids could take place, and where there were inlets, but no 

 outlets, save a small degree of expansion. 



The only comment on the circumstance is the following sentence : — " It 

 appears from this, that the growth of trees in diameter is the result of a local 

 developement ; and that the organic matter of this increase does not descend 

 from the upper parts of the trunk, as some physiologists still think." Whether 

 this sentence was written by the reporter to U Hermes, or by M. Dutrochet 

 himself, does not appear ; but, if by the latter gentleman, it will astonish many 

 of his own admirers, as well as all those who consider the descent of the sap 

 as an irrefragable truth. — J. Main. March 14. 1837. 



Introducing the better Sorts of Vegetables to Cottagers. (Vol. XI. p. 63.) — I 

 believe we need not trouble ourselves much about introducing the better sorts 

 of vegetables to cottagers. I find many who cannot endure that general 

 favourite, celery ; and 1 have amused myself to-day on the subject with a man 

 at work here. I sent him some salad, nicely dressed for my own dinner, to 

 try and make him like celery and beet-root. Even the dressing did not make 

 it palatable to him, nor conquer his objections to the celery and beet-root ; and 

 we had a hearty laugh together, when he closed the description of his dislike 



