On the Theory of Manures. 17 



inferior, not suiting the season. One part of the field, equally 

 good with the other and as well manured, may fail also from 

 tids of weather being against it, one piece being worked on a 

 dry day, the other on a wet ; one piece or one field being- 

 farther advanced -than another, and not suffering so much from 

 drought as the other, the soil being more retentive in one place, 

 and more open and jDorous in another. If all these are not 

 j)roperly taken into account, the observation is imperfect ; and 

 some of them may, from circumstances, have eluded the ob- 

 servation of the most vigilant. There must be causes for every 

 thing, but we must wade through much difficulty in arriving at 

 them before we can furnish proper data, and must not expect 

 mathematical results where so many obstacles, seen and unseen, 

 are in the way. 



The best experiments for ascertaining the true nature of the 

 action of these substances are those made by Mr. Fortune in 

 the Society's Experimental Gardens. He washed silver sand 

 as a soil for plants, to prevent any effect from previous organic 

 remains ; and also washed the roots of the geraniums he planted 

 in the sand. The result was, that none of the various sub- 

 stances he watered with in solution had any more effect than 

 common water, except carbonate of ammonia and wood-ashes 

 mixed, which contain the most of the constituents generally 

 needed in plants. In some potted in common soil, the other 

 substances produced the usual effect. Before any action can 

 take place, it is evident that real food containing all the con- 

 stituents of plants must be supplied from some source, and 

 these substances will always be most generally valuable. Such 

 as sulphuric acid, which is found only in very small quantities, 

 unless in some particular kinds of plants ; and such as muriatic 

 acid *, of which only a trace is to be found ; must be much less 

 needed than carbonic acid, and must act principally by their 

 influence on the constituents of food, either in the soil before 

 absorption, or in the transformations going on in the plant. 

 Such bases as iron are prejudicial, unless in very small quan- 

 tity ; such as magnesia and alumina are very little needed as 

 constituents, and must be sometimes hurtful in excess. Potash 



* The experiments of Mr. Solly on muriatic acid, lately recorded in the 

 Gardener''s Chronicle, show that, so far from being injurious, as formerly sup- 

 posed, and poisonous to plants, he found it beneficial, even in pretty large 

 quantities. He found it, also, to have the effect of requiring much less water 

 to the pot the plant experimented on was growing in ; the usual perspiration 

 of the plant being much checked, either by the stopping of the pores, or pre- 

 venting the extrication of water chemically. Some pots naturally require 

 much more water than others, but this is likely to have been observed. 

 Acids, generally, are prescribed to check perspiration in human beings ; if 

 acids have the same effect on plants, it may be found another circumstance 

 requiring attention. Such an action cannot, certainly, be gcnerallv beneficial. 



3d Ser. — 1843. I. c 



