THEY MAY COUNTERACT EACH OTHER. 59 



to our cultivated crops, must be made upon soils which are 

 " in fair order.' 1 ' 1 It is stated by Mr Main, as the result of his 

 trials, " that if other circumstances, such as weather, &c., 

 conspire to injure a crop, -and at the same time the soil wants 

 condition, top-dressing will not be followed with satisfactory 

 results." And this is only expressing, in the language of a prac- 

 tical man, the scientific truth, that to enable any plant to grow 

 well, all the materials it requires must be placed within its easy 

 reach. 



3. Influence of one substance in counteracting the beneficial 

 action of another. 



This point, though closely connected with the subject of the 

 preceding section, is interesting and important enough to de- 

 serve a separate consideration. 



I shall have occasion hereafter to show, that certain mixtures 

 of saline substances applied to the land, act, generally speaking, 

 in a more favourable manner than any of the same substances 

 applied singly. This is consistent with our theoretical know- 

 ledge, and is readily enough explained. But such experiments 

 as we at present possess seem to show that some substances, 

 when applied together, may produce a less effect than one 

 or other of them applied singly. Thus in some experiments 

 upon wheat, made under the direction of Lord Blantyre, at 

 Lennox Love, rape-dust, common salt, and sulphate of soda 

 were applied singly, and in conjunction, with the following 

 results : 



Increase per Decrease per 

 acre. acre. 



Rape-dust, 16 cwt. per acre, gave . 3^ bush. 



Sulphate of soda, 1 cwt. . . 9^ bush. 



Common salt, 1 cwt. . . . 1^ ... 



Rape-dust and sulphate, | of each, 3 



Rape-dust and common salt, ^ of each, 2J ... 



In these results it appears that the natural good effect of 

 rape-dust was lessened considerably when mixed with the given 

 weight of common salt, and that the influence of sulphate of 

 soda for evil was able to overcome entirely that of rape-dust for 

 good, and to cause a loss instead of a gain on the whole. 



