102 



HiSTO-CHEMICAL KeSEARCHES ON THE FaLL OF LeAVES IN 



Autumn. 



By Dr. K. Ledeganck. 



Translated, and abridged, by B. D. Jackson, F.L.S., F.E.M.S., from tbe 

 " Bulletin de la Societe Eoyale de Botanique de Belgique," torn x. 

 No. 3. 3rd June, 1872. 



{Read November 22nd, 1872.J 



1,— Historical. 



A fact wortli remarking in the history of the sciences dependent 

 upon observation, is the reluctance with which the experimental 

 method is introduced, and the cautious use the first workers have 

 made of it, to resolve the problems relative to the vital functions of 

 plants and animals. 



This statement receives a full and entire confirmation in the 

 history of the subject before us. The fall of the leaf in autumn, a 

 phenomenon which strikes even the unobservant by its regular 

 occurrence, and by the remarkable change produced by it each year 

 in the face of nature, is still one of those questions hardly glanced 

 at by a large number of writers, who usually pass it over in silence, 

 or to explain which, they have been satisfied, for a long period, to 

 offer hypotheses as diverse, as they are unsafe. 



It is true that we are no longer in the same plight as when 

 Ingenhousz (1779) explained the phenomenon in question by a 

 final cause, having for an object the preservation of the human race, 

 thus : — " When the cold of winter stops the universal tendency to 

 decay, we have no need of the assistance of leaves to purify the 

 atmosphere, which is no longer infected. The leaves falling, and the 

 tree continuing to live without them, tells us that they have more 

 to do with our conservation than that of the tree." 



Mustel believed it was purely mechanical, and in the domain of 

 hydro-dynamics. The transpiration by leaves being suspended in 

 autumn, the ascending sap accumulates in the leaf, petiole, and axis. 

 From this results a strong interior pressure, which has the effect 



