1D2 Disease in Plants. 



and potash into use which previously had been inoperative ; the 

 deficiency of potash, however, interfered with a development 

 of tubers proportionate to that increase in tops which was pro- 

 moted by the abundance of magnesia and lime. 



In this way is explained the enormous addition to the yield of 

 tops and the comparatively small increase in the crop of tubers, 

 consequent on the use of the manure. 



In Box III., where the turf was manured with alkalies, lime, 

 and phosphoric acid, the quantity of potash increased, and 

 ammonia completely excluded, the growth of the plant was 

 stimulated in a very different direction. Although the turf had 

 received only half as much phosphoric acid as that in Box II., 

 yet the additional potash (although only 3-lOths per cent, of the 

 whole mass of soil) brought about an entirely different proportion 

 in the produce of tubers and tops. 



Subtracting the crop of Box III. from that of Box I., the 

 excess is found to be 1038 gramines of tops and 4681 grammes 

 of tubers. The relation between tubers and tops was : — 



Tubers. Tops. 



On the whole produce ..10 .... 4 



On the increase .. ..10 .. .. 2 



These facts, as well as those supplied by the bean-experiments 

 already mentioned, appear to me to be very instructive with 

 regard to the relative growth (vegetations — verhaltnisse) of our 

 cultivated plants, their proportionate or disproportionate develop- 

 ment, and pave the way for a full understanding of them by- 

 and-by. 



Every experiment hitherto directed towards the determination 

 of the influence of special elements of plant-food has been almost 

 without value in consequence of its having been tried on soils of 

 unknown composition ; for this, of course, made it exceedingly 

 difficult, if not impossible, to estimate the share taken by the 

 elements already present in the soil in producing the observed 

 results. 



I believe that it is only by experiments on the growth of 

 different cultivated plants in soils of knoion composition that a 

 precise knowledge can be gained of the influence wrought by 

 the diminution or increase, by the lack or excess, of special 

 fertilisers in the soil upon the total produce, as well as upon 

 special functional developments of the plants, such as their grain 

 or straw, tubers or roots. 



It stands to reason, that, if this influence is exactly known, the 

 agriculturist will in future be in a better position to judge of 

 the quality of his soil from the produce of his field, — the relative 

 proportions of corn and straw, of stems and roots which it yields. 

 It will thus become easy for him to select the manure best fitted 



