THE 



PHILOSOPHICAL MAGAZINE 

 AND JOURNAL. 



31 st OCTOBER 1824. 



XLI. On the Theories of Vegetation of Sir J. E. Smith and 

 M. du Petit-Thouars. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



"JX/fY friend Mr. John Lindley has, in your Number for 

 -*-"-*• August last, given a very clear and comprehensive de- 

 tail of the theory of vegetation proposed by the ingenious 

 M. Aubert du Petit-Thouars, which I have there perused for 

 the first time, with peculiar pleasure. It is highly satisfactory 

 when the observations and speculations of different physiolo- 

 gists confirm each other, without any communication between 

 the parties ; and I cannot but congratulate myself that the 

 theory of the French philosopher in question, whose high 

 character I well know, establishes, in every essential point, 

 that published in my Introduction to Botany, of which the 

 first edition appeared in 1807. The old hypothesis of Du 

 Hamel and others, of the sap being conveyed through the 

 woody fibres, had never satisfied me, and I have been accus- 

 tomed, in my earlier Courses of Lectures, to show its insupe- 

 rable defects. Dr. Darwin, and especially Mr. Knight, by 

 their remarks and experiments, confirmed by my own obser- 

 vations, have long ago convinced me, that the spiral-coated 

 vessels of plants convey their sap, or blood, into the leaves, 

 there to be acted upon by air, light and heat, so as to form 

 secretions of wood, bark, and succi proprii, by the returning 

 vessels. I believe I first suggested, in the above work, that 

 the supposed vernal flowing of the sap is altogether an error, 

 and that there is no running of that fluid along the vessels of 

 a plant, before the leaves open, and then no real circulation ; 

 the discharge of sap from a wounded tree in spring being no 

 more than what is caused by the accumulated irritability of 

 the vegetable body during winter. But I beg leave to refer 

 your leaders to the work itself, of which a filth edition, cor- 

 rected and enlarged, is now printing. 



Mr. Lindley must have read my book, and I should have 

 Vol 64. No. 31 8. Oct. 1824. II h expected 



