SOILS. 



139 



merit nitrogen, and would therefore form the 

 richest mould on their decomposition. The 

 average amount of nitrogen in the seventeen 

 descriptions of leaf is 0*87 per cent. It must, 

 however, be remembered that autumn leaves 

 are necessarily comparatively poor in nitrogen, 

 potash, and phosphoric acid, since these con- 

 stituents pass out from the leaves into the body 

 of the tree with the approach of winter, there 

 to be held in store for next year's use. In one 

 sense it would be perfectly correct to say that 

 dead autumn leaves, even those that have never 

 been bleached by rain, have been well-nigh 

 exhausted of their most valuable fertilizing con- 

 stituents. But, as is well known, considerable 

 quantities of the less valuable kinds of ash in- 

 gredients, notably silicic acid and lime, together 

 with certain proportions of the more valuable 

 constituents, still remain in fallen leaves. 



The next table shows the amount of some 

 selected constituents contained in certain plants, 

 or portions of plants, which may be employed 

 in the production of humus matter of horti- 

 cultural soils. 



Selected Constituents in 100 of Vegetable Sxibstance. 









Phos- 





Description of Plant. 



Water. 



Nitrogen. 



phoric 

 Acid. 



Potash. 





per cent. 



per cent. 



per cent. 



per cent. 



Heath, 



20 



0-9 



o-io 



0-40 



Fern, 



16 



2-4 



0-45 



2-40 



Furze, 



16 



2-5 



0-23 



0-80 



Horsetail, 



14 



1-8 



0-41 



270 



Rushes, 



18 



1-1 



0-12 



0-43 



Moss, 



25 



10 



0-16 



0-29 



Leaves of Beech, . . . 



15 



0-8 



0-24 



2-58 



,, „ Oak,. ... 



15 



0-8 



0-34 



2-02 



„ Fir, 



174 



0-5 



0-20 



0-54 



„ Pine, 



134 



0-8 



o-io 



0-46 



,, ,, Spruce, ... 



12| 



0-9 



0-20 



1-60 



These facts teach us that the fertility of soils 

 is due to the richness of the organic residues of 

 previous generations of plants, mixed with cer- 

 tain mineral substances, the most important of 

 which are phosphoric acid and potash. 



Little by little, under the combined influence 

 in the soil of moisture and warmth, and the 

 action of bacteria, the compound organic nitro- 

 gen of vegetable matter is transformed, and 

 becomes the protean nucleus of microbes, which 

 reproduce themselves with extreme rapidity, 

 having for their object the carrying on of the 

 work of oxidation and conversion from insoluble 

 to soluble plant-food. 



The next table illustrates the composition of 

 three different descriptions of mould used for 

 horticultural purposes. 





Leaf- 



Forest- 



Peat- 





mould. 



mould. 



mould. 





percent. 



percent. 



per cent. 



Organic matter (humus), 



17-00 



8-40 



18-80 



Clay and silica (sand), 



79-80 



63-34 



76-05 



Nitrogen, 



0-50 



0-45 



1-40 



Potash, 



0-31 



073 



0-31 



Phosphoric acid, 



0-06 



o-io 



0-20 



Lime, 



0-19 



2-08 



0-55 



Magnesia, 



— 



1-71 



— 



Soda, . 



— 



010 



— 



Iron oxide, 



0*26 



4-98 



0-20 



The first point to observe is, the large quantity 

 of organic matter present in these soils — in the 

 leaf -mould 1 7 per cent, in the peat-mould nearly 

 19 percent, and in the forest-mould 8 J percent. 

 In some samples of fertile mould the amount of 

 organic matter will not be more than from 1 \ to 2 

 per cent, while in the famous black soil of Eussia 

 it varies from 5 to 12 per cent. It is also seen 

 that these soils contain a large proportion of 

 nitrogen, the leaf and forest moulds containing 

 nearly four times as much as the average of 

 ordinary arable soils, while the peat -mould is 

 considerably more, but much of the nitrogen in 

 the peat would be in a very inert condition. 



The next table shows the composition of two 

 leaf-moulds from France, and of one from Ghent, 

 as employed in the horticultural establishments 

 of those countries. 



Composition of Leaf-moulds (by Georges Truffaut). 





From Pam- 



From 



From 





bouillet, 



Maurepas, 



Ghent. 





France. 



France. 



Belgium. 





per cent. 



per cent. 



per cent. 



Organic matter (humus), 



9-53 



17-00 



64-00 



Clay and silica (sand),... 



83-60 



. 80-55 



34-10 



Nitrogen, 



0-59 



0-47 



1-17 



Phosphoric acid, 



0-12 



0-13 



0-16 



Lime, 



0-26 



0-18 



0'35 



Potash, . ... 



0-35 



0-50 



0-14 



Iron oxide, 



— 



0-17 



— 



The moulds from France correspond much 

 more exactly with those used in England than 

 does that from Belgium, which contains an 

 enormous percentage of humus matter, and is 

 in fact a peat-mould. Now, one of the most 

 delicate points in horticultural chemistry is 

 whether the humus of the soil is or is not 

 directly absorbed by the growing plant. De 

 Saussure concluded that air and water contri- 

 buted a much larger proportion of the dry 

 substance of plants than did the soils in which 

 they grew. In his view a fertile soil was one 

 which yielded liberally to the plant nitrogenous 

 compounds and mineral ingredients: whilst the 

 carbon, hydrogen, and oxygen of which the 

 greater proportion of the dry substance of the 

 plant was made up, were mainly derived from 



