DR. DAUBENY ON THE ROTATION OF CROPS, ETC. 



187 



racter, still the failure of the second and third crops of Euphorbia would seem attri- 

 butable to some deleterious influence exerted by the excretions of the antecedent 

 crop, rather than to the ground having become exhausted, inasmuch as the latter, 

 without being in the meanwhile enriched with manure, proved its ability to produce 

 tolerable crops of other vegetables. 



The acrid nature of the juices of the Euphorbia may possibly explain, why this plant 

 should constitute an apparent exception to the rest, for it will be seen, that in all the 

 other cases, the diminution in the amount of produce, consequent upon the continua- 

 tion of the crop from year to year, was only such as might be supposed to result from 

 a falling off in some one of those ingredients which were necessary for its develop- 

 ment, and was not of a nature to indicate the existence of anything poisonous in the 

 soil in which it grew*. 



I shall therefore now proceed to state the amount of produce obtained during the 

 several years from each of the remaining plants above enumerated, distinguishing the 

 crop which was repeated year after year in the same plot of ground as the permanent 

 one, and that which was grown successively in different parts of the garden as the 

 shifting one. 



1. Solanum tuberosum. — Ground not manured since 1833. 



1840. In this year it occurred to me, that it might be interesting to determine what 

 difference, as to the amount of produce, would be produced by planting in one in- 

 stance tubers from the crop obtained the year before in the same plot, and by employ- 

 ing in another those raised in some different locality. 



The difference in quantity will be seen not to be very considerable. 



* It can hardly, I think, be denied, that juices are excreted from the roots, as well as taken up by them ; 

 the only question is, are these excretions injurious to the plants of the same species which grew in the soil 

 afterwards, and if they are, are they favourable to the growth of others } The first of these positions may be 

 countenanced by the facts detailed in the text, but the latter is little, if at all, corroborated by them. 



MDCCCXLV. 



2 c 



