PROCKKDINGS OF TIIF. 



of other jilants, on nnIui Ii tlir t'xiTotions iiiij;lit produce no bad 

 effects. Amongst the exporiiiients most connnonly (|iioted in 

 proof of the theory of excretions are tliose of Macaire, who 

 thou^tit he had ascertained by positive and iMKjuestionable expe- 

 riments tlnit the roots of plants possess the ])ower of excretion ; 

 and accordingly the theory received very general credence ; re- 

 cently however doubt has been thrown on his coiu lusions by the 

 experiments of M. Hraconnot, wlio has rejjcated the ex})eriments 

 of Macaire with threat care, and has arrived at the conclusion 

 that the substances \vhi(h the latter thought were excretions 

 were in reality only the natural juices of tlie plant, which, from 

 the mode in which the experiments were conducted escaped in 

 consequence of the accidental rupture of the fine fibres of the 

 roots. The theory of excretions therefore requires new proof 

 before it can be admitted as established ; yet it is hardly 

 justifiable wholly to reject it, since there yet exist many facts 

 which make it appear i)robablc. 



Reference has just been made to the formation of organised 

 tissues, and the connection existing between the assimilation of 

 carbon, oxygen, and hydrogen, and the formation of proximate 

 principles ; what was said on that subject might be equally ap- 

 plied to the formation of colouring and odorous matters in 

 flowers and plants. The circumstances which influence or mo- 

 dify these secretions, nay even the very conditions requisite to 

 their production, are unknown. If the study of this part of the 

 subject is less important practically, it is of nearly equal interest 

 in a scientific point of view. 



Such were a few of the many subjects requiring investigation, 

 and the study of which promised valuable results, when the Che- 

 mical Committee of the Horticultural Society was appointed. It 

 was, however, evident to the Committee that it was impossible to 

 take up more than one of these branches of inquiry at once. In 

 order to arriv'e at good and trustworthy results, it was necessary to 

 confine attention to a few great points, and to investigate them by 

 numerous experiments, carefully repeated, and so varied that the 

 results they led to might be unciuestionable, and furnish correct 

 data for future inquiry. The connexion between the earthy matters 

 of the soil and the plants which are grown in it, is less perfectly 

 understood, than any other part of the chemistry of vegetation. 

 That subject therefore seemed one most worthy of early exa- 

 mination, because it embraced the great leading principles of 

 both agriculture and horticulture, and promised to be of great 

 value, in preparing a way for future experiments. 



It is unnecessary to observe to the scientific reader that this 

 investigation is one of no trifling labour, and that thousands of 



