Essay oil Physiological Botany : — Sap. 257 



Art. V. Afi Essay on Physiological Botany, in Continuation of 



ike Experimeiits described in the preceding Paper. By Mr. Joseph 



Thompson. 

 Sir, 



After four years more of extensive practice, and close at- 

 tention to the ordinances of nature in tliis branch of my pro- 

 fession, I am satisfied that the present theoretical system of 

 vegetable phenomena was founded in error by Malpighi and 

 Grew. Had they commenced their experiments earlier in the 

 season, and wounded the extremities of the branches, they 

 would have obtained pure limpid sap many days before they 

 got it in the cylindrical wimble holes, in which they never 

 could discover from what part of the cylinder it was produced, 

 the accumulation would only appear in the lower segment of 

 the cylinder, which naturally led to the supposition that it was 

 propelled upwards. 



The late Sir James Edward Smith, in his Introduction to 

 Physiological and Systematic Botany,^ has brought into view 

 most of the experiments made on this subject, from the time of 

 Malpighi down to those of Thomas Andrew Knight, Esq., 

 whose experiments on the cuttings of fig trees are recorded in 

 ihe Transactiom of the Philosophical Society of 1801, 1803, 

 and 1804, 



The Rev. Mr. Keith has also collected all that has been 

 written on this subject. The experiments conducted and re- 

 lated by those very scientific persons do not, however, appear 

 to me satisfactorily to establish the conclusions that have been 

 drawn from them, and I now proceed to add to my former 

 observations on this subject a statement of facts which seem 

 to impugn their solidity. 



Sir J. E, Smith, in his book above quoted, says, " much 

 contrariety of opinion exists on the vascular system of plants, 

 propulsion of sap, &c." The excellent plates of Anthony Tod 

 Thomson, in his Lectures on Botany, show that the anatomy 

 of plants and the vascular system are correctly understood ; 

 but the propulsion of sap, its change to cambium and deposit 

 in wood, the time occupied, and temperature most congenial 

 to those operations in the vegetable system, are clouded in 

 darkness. 



The following quotations will show that some writers have 

 accidentally hit upon the true system, in so far as regards the 

 primary motion of the sap. 



In Miller's Gardener's Dictionary, second edition, printed 

 in 1741, under the article Persicum (Peach), he says: " It 

 sometimes happens that the' roots are buried too deeply; for the 

 sap which is contained in the branches being put strongly in 



Vol. V. — No. 20. s 



