138 



THE GARDENER'S ASSISTANT. 



manure. The best form in which phosphoric 

 acid may be added to leaf-mould is that of pul- 

 verized bone-phosphate. Phosphate of potash 

 is also excellent. Superphosphates yield a cer- 

 tain proportion of phosphoric acid soluble in 

 water, but in leaf-mould culture they are not to 

 be recommended, being almost always acid, and 

 this introduction of sulphuric acid into soils 

 poor in lime would be certainly hurtful. 



Potash. — Leaf -mould contains a considerable 

 proportion of potash, which is only slowly avail- 

 able for vegetation. For certain cultivations, 

 especially that of Ferns, potash manures have 

 a very beneficial effect when applied to leaf- 

 mould. The most rational method is to use 

 carbonate of potash, and to apply it dissolved 

 in water to the soil to be manured; this salt is 

 retained by the soil, and the plants are able to 

 absorb it as they need. The proportions to be 

 used vary according to the requirements of the 

 plants cultivated. 



Different Soils employed in Horticulture. — In an 

 interesting paper by Georges Truffaut, on the 

 chemical and physical properties of different 

 soils employed in horticulture, the author rightly 

 remarks that the exact knowledge to the 

 gardener of the composition of the moulds he 

 cultivates is very important, and that for several 

 reasons, not the least being that this knowledge 

 enables him to use complementary manures for j 

 forcing purposes, and to adapt the supply to the 

 requirements of the particular plant he wishes 

 to raise. 



In dealing with the question of the formation 

 of soils we have already shown the important 

 part played by decomposing vegetable sub- 

 stances. The humus, or decayed vegetable 

 matter of all soils, has its origin, as we have 

 also seen, in the dead leaves, roots, &c, of pre- 

 vious vegetation. It is continually forming 

 wherever plants grow. It is, in fact, the founda- 

 tion, and often the entire source, of the organic 

 substances in soil. 



Each year a certain portion of the vegetable 

 growth dies off — leaves and branches fall, and 

 parts of the roots decay. Some of the organic 

 substances which fall upon the surface of the 

 ground returns again to the atmosphere; but a 

 certain part remains, and, added to that which 

 decays underground, becomes, as it oxidizes, 

 available for future growth. The atmosphere 

 of the soil, which at first differed but little from 

 that which exists above it, becomes highly 

 charged with carbonic acid, which decomposes 

 the minerals — lime, potash, magnesia — in the 

 soil, and thus, year by year, more and more of 



the nitrogen collected by each generation of 

 plants becomes available for the generation that 

 succeeds it. 



The following table will illustrate the increase 

 of nitrogen formed during the process of fer- 

 mentation and decay of certain selected vegetable 

 products : — 





Nitrogen per cent. 















Product Examined. 



In 



Decom- 



Increase 



Authority. 





Original 



posed 



of Nitro- 







Plant. 



Organic 

 Matter. 



gen. 





Meadow hay, ... 



1-62 



4-42 



2-80 



Kostylcheff. 



Clover, 



2 00 



5-28 



3-28 





Maize plant, ... 



1-88 



4-50 



2-62 





Cereal straw, ... 



1-27 



2-10 



0-83 





Dogwood leaves, 



1-30 



470 



3-40 



Mayer. 



Oak leaves, 



0-80 



470 



3-90 



Truffaut. 



Heath, ... 



0-20 



5-10 



4-90 



» 



It will be observed that there is an increase in 

 the amount of nitrogen formed during the decay 

 of the vegetable substances mentioned, ranging 

 from 0*83 per cent in the cereal straw, to nearly 

 5 per cent in heath. 



Deep beds of vegetable mould are frequently 

 met with in forests under trees, and on dry 

 land generally, wherever vegetation is rank and 

 neglected. 



It is found that the differences in the chemical 

 composition of the original materials, whether 

 of rocks or of vegetable matter, which compose 

 a soil, mainly account for the enormous varia- 

 tion existing in the different soils under culti- 

 vation, and of the amount of organic matter 

 (humus) and of nitrogen which they contain. 



The next table shows the amount of nitrogen 

 contained in the leaves of certain trees while in 

 a fresh condition. 



Nitrogen in 100 parts of leaves of — 







Maple, 



. - 98 per cent. 



Plane, 



. 0-89 



,, 



Horse-chestnut, 



. 0-54 



,, 



Acacia (Robinia), 



. 1-05 



,, 



Lime, ... 



. 0-96 



,, 



Service, 



. 0-88 



,, 



Ash, 



. 0-84 



,i 



Oak, 



. 0-80 



5 J 



Hazel, 



. 0-65 



,, 



Plum, 



. 1-08 



,, 



Poplar, 



. 0-98 



,, 



Willow, 



. 1-28 



,, 



Birch, 



. 0-52 



,, 



Elm, 



. 074 



J> 



Alder, ... 



. 1-36 





Fir 



. 0-57 



5 J 



Catalpa, 



070 



J> 



Average, 



0-87 per 



cent. 



It is seen that the leaves of the Acacia, Plum, 

 Willow, and Alder are the highest in the ele- 



