238 Dr Daubeny on the Writings and 



series of tints, which the flowers in each species may be 

 brought to assume, founded upon the same chemical principles, 

 and confirmed by observing the degree in which art is capa- 

 ble of modifying their natural colour. 



Both these theories were suggested in the Flore Fran9aise 

 published in 1805 ; and whilst the former has since been con- 

 firmed by the researches of Macaii'e, respecting the chromule 

 of the leaf, the latter has been more fully developed by 

 Schubler and Funk in a memoir published by them at Tu- 

 bingen in 1825. 



One of the ablest chapters in the work, may perhaps be 

 considered the one in which he discusses the cause of the di- 

 rections which the parts of plants severally affect. 



He has here proceeded upon the sound, but too often ne- 

 glected, principle, of declining to call in the aid of the vital 

 principle, for the purpose of explaining phenomena which may 

 be referred to physical causes alone. The maxim, " Nee Deus 

 intersit,'' holds good in the natural sciences not less than 

 in poetry. 



Thus, instead of vaguely attributing the tendency of the 

 stem to mount upwards, and that of the root to descend, to any 

 principle so near akin to instinct or volition, as that of a dis- 

 position in the one to seek, and the other to avoid light, as 

 some former physiologists had done, Decandolle shews, that both 

 these phenomena would arise out of the difl^erence in the mode 

 of growth belonging to these two parts, and out of that in the 

 way which certain external agents afffect theii' organization. 



Nor has our author been less successful, in applying those 

 principles of vegetable physiologj'^, which he had previously 

 laid down, to the explanation of the differences which subsist 

 between the various kinds of parasitical plants, and in estab- 

 lishing a classification of them founded on the above consi- 

 derations. 



He has pointed out that those parasites which insert their 

 roots into the woody matter of the plant which nourishes 

 them, require leaves, because they obtain the sap unelaborated ; 

 whilst those which are rooted merely into the bark, are desti- 

 tute of leaves, because they draw their supply from the de- 

 scending sap, which has already undergone the necessary pre- 

 paration in the parent tree. 



