of the Hotation of Crops. 15 



enough to be able to adduce proof of the priority of the hypo- 

 thesis of the Domestic Gardener's Manual to that now ascribed 

 to M. de Candolle. That learned professor may have presented 

 enlarged views of the theory, he may have added fact to fact in 

 corroboration thereof; but still his claim to originality falls to 

 the ground. 



It is not contended that the necessity of a change of crops is 

 a new theory ; far from it : the practice is proved by fact to be 

 more or less expedient. Let me not be mistaken ; what I argue 

 for is simply this : that the theory of a fecal exudation of some 

 matter by the roots, saturating the soil, and rendering it poisonous 

 or unwholesome to the individual, but nutritive and salubrious 

 to some other plant, is new ; and appears never to have been 

 advanced, or even hinted at, until I wrote the passage extracted, 

 as above, from my work. 



I do not for a moment desire to detract from the ability or 

 authority of so able a botanist as De Candolle; but, great and 

 deservedly high as his name and reputation may be, I, a com- 

 paratively nameless writer, cannot abandon the consciousness 

 that I penned, from my own unassisted observations and reflection, 

 in 1829, those remarks that now form the sum and substance of 

 what is considered a neia theory. I have supposed it possible 

 that Brugmans may have anticipated me and every one else; but, 

 even in this case, as was before hinted, what becomes of the 

 present claim ? But I have good reason to believe that the fact 

 was not so ; for, in a letter very recently received from the pre- 

 sident of the Horticultural Society, that gentleman observes : — > 

 " The Continental naturalists have lately imagined that trees emit 

 some matter into the soil, of the nature of excrement, which sub- 

 sequently becomes noxious." If, then, the doctrine be deemed 

 recent, the priority ought to rest with one who wrote nearly four 

 years anterior to the publication of the theory which is thus 

 blazoned forth as new. I quit this part of my subject, in order 

 to allude to matters of pleasing interest in the other parts of the 

 article by the reviewer. 



It appears that M. Macaire has made many experiments to 

 confirm the theory of the exudation of matter from the roots. 

 He is stated to have ascertained the fact from a comparison of 

 results, in attempting to raise plants " in pure siliceous sand, 

 pounded glass, washed sponge, white linen, and particularly in 

 rain water. After cleansing the roots thoroughly, he placed 

 them in pure water. After they had put forth leaves, expanded 

 their flowers, and flourished for a time, he ascertained, by the 

 evaporation of the water, and the use of chemical reagents, that 

 the water contained matter which had exuded from the roots." 

 I cannot allow myself space to quote the experiments at large. 

 One, however, with the bean (Ficia .Faba) must be noticed. 



