THE CHEMISTRY OF GARDEN CROPS 197 



ten ; sulphuric acid, fourteen. The Beet : phosphates, fourteen ; 

 potash, forty-nine ; soda, nine ; salt, twenty ; lime, six ; sulphuric 

 acid, five. 



As a matter of course, Lentils and other kinds of pulse agree 

 more or less with Peas and Beans in the predominance of phosphates 

 and potash. So, again, all the Brassicas, whether Kales, Cauliflower, 

 or whatever else, agree nearly with the Cabbage in a predominance 

 of lime and sulphur ; ingredients which fully account for the offensive 

 odour of these vegetables when in a state of decay. Fruits as a rule 

 are highly charged with alkalies, and are rarely deficient in phos- 

 phates ; moreover, stone-fruits require lime, for they have to make 

 bones as well as flesh when they produce a crop. As regards the 

 alkalies, plants appear capable of substituting soda for potash under 

 some circumstances, but it would not be prudent for the cultivator 

 to assume that the cheaper alkali might take the place of the more 

 costly one as a mineral agent, for Nature is stern and constant in her 

 ways, and it can hardly be supposed that a plant in which potash 

 normally predominates can attain to perfection in a soil deficient in 

 potash, however well supplied it may be with soda. The cheaper 

 alkali in combination with salt may, however, be usually employed in 

 aid of quick-growing green crops ; and more or less with tap-roots 

 and Brassicas. As regards Potatoes, it seems worthy of observation 

 that they contain but a trace of silica, and yet they generally thrive 

 on sand, and in many instances crops grown on sand are free from 

 disease and of high quality, although the weight may not be great. 

 The mechanical texture of the soil has much to do with this ; and 

 when that is aided by a supply of potash and phosphates, whether 

 from farmyard manure or artificials, sandy soils become highly pro- 

 ductive of Potatoes of the very finest quality. On the other hand, 

 Potatoes also grow well on limestone and chalk, and yet there is but 

 little lime in them. Here, again, mechanical texture explains the 

 case in part, and it is further explained by the sufficiency of potash 

 and phosphates, as also of magnesia, which enters in a special 

 manner into the mineral constitution of this root. 



Thus far we have not even mentioned nitrogen, or its common 

 form of carbonate of ammonia ; nor have we mentioned carbon, or 

 its very familiar form of carbonic acid. These are important ele- 

 ments of plant growth ; and they account for the efficacy of manures 

 derived directly from the animal kingdom, as, for example, the drop- 

 pings of animals, including guano, which consists, in part at least, 

 of the droppings of sea-birds. The nitrogen in these substances 



