14C) JOl'RNAL 01- THE ROYAL HORTICULTURAL SOCIETY. 
plant-roots and the total reserve of potash contamed in the soil. On the 
other hand, the use of potash gives, on the whole, such wonderful results 
that it is difficult to gauge the advantage which may in many cases arise 
from the use of potassic manures. It is certain, however, that such are ' 
often indispensable. "^Vo have seen, indeed, that certain crops demand 
between 150 and 200 kilos, of potash per hectare per annum. On the 
other hand, experiments made with the drainage water have shown that 
1,890 cubic metres of water having filtered through a clayey soil have 
in one year only carried away 9*374 kilos, of potash. I have adopted 
the conclusions of M. Schloesing, who thinks that there may be considered 
as immediately useful that portion of potash which is set at liberty by 
treating the soil (cold) with a quantity of acetic acid just sufficient to 
coagulate the clay and decompose the humates. Here are some figures 
relating to the quantity of potash contained in a certain number of our 
horticultural soils : — 
Soluble rot^isli Soluble Potar,h 
Soils. in aqua rt ^ia at in acetic acid 
bnilinp point. cold. 
Rambouillet Leaf-mould . . 3-50 per 1.000 ... 0-780 per 1,000 
Maurepas Soil .... 4-98 „ ... I'OOO 
Ghent Soil 1-43 „ ... O'Slo 
Peat-mould 3-06 „ ... 1-390 
Maurepas . . . 3-06 „ ... 1-390 
Trap Loam 4-76 ,. ... 2-090 
which figures show that in the majority of cases potash is an element of 
which the manurial value is much less than that of nitrogen or phosphoric 
acid. 
Lime. — Lime plays a part of the first importance from the point of 
view of vegetable alimentation. If in many cases lime may serve but an 
insignificant part purely as an aliment, it seems nevertheless necessary to 
have it present in sufficiently large proportions to saturate, and fix in 
the tissues, the organic acids which form the salts (such as the oxalate 
and citrate of lime), which crystallise ; and which are found very frequently 
under microscopic research. 
It may be observed that when lime is absent it is potash which 
takes its place. We have seen that lime arises from the decomposition 
of the silicates (disintegration of felspaths of the oligoclase type). Lime 
is sometimes, but rarely, found in the form of silicates. In this con- 
dition it is almost unutilisable by plants. Lime is chiefly met with in our 
soils in the form of carbonates, sulphates, and combinations with humic 
acid. When a soil contains much humus and little lime the greater part 
of this element is then found in the form of humate of lime. This com- 
plex mixture is extremely favourable to the development of the various 
micro-organisms. When a soil is found to contain humate and carbonate 
of lime in association, it is usually extremely fertile. It is not so when 
the lime is principally in the form of sulphate. Beyond a certain limit 
cultivation in a soil with an excess of sulphates becomes difficult. When 
the sulphate of lime is proportionately small, and especially in clayey 
soil, it plays a most important part in enhancing the solubility of the 
potash contained in the clay. The sulphate of lime in presence of silicate 
of potash and alumina irives rise to sulphate of potash and silicate of 
lime. The sulphate of potash is very soluble in the presence of carbonate 
of lime in the soil : it is again decomposed, and there is then produced 
