SOILS. 



271 



change in the constituent parts of a soil will 

 cause the plants of one soil naturally to affect 

 another, a circumstance every plant cultivator 

 knows from experience. 



Taking soils in the order in which we have 

 already placed them, we find that in 



Argillaceous soils, Saponaria officinalis, Orobus 

 tuberosus, Lotus major, Carex (many species), 

 Juncus (many species), Tussilago farfara, Poten- 

 tilla reptans, P. anserina, P. argentea, Thalic- 

 trum flavum, Spiraea ulniaria, Aira csespitosa, 

 Equisetum arvense, &c, exist. 



In Calcareous soils, Onobrychis sativa, Clema- 

 tis vitalba, Veronica spicata, Verbascum lych- 

 nitis, Lithospermum officinale, Campanula glo- 

 merata, Phyteuma orbiculare, Helianthemum 

 vulgar e, abound. 



In Silicious soils, Veronica verna and most of 

 the annual speedwells, Silene Anglica, Echium 

 vulgare, Herniaria glabra and H. hirsuta, Are- 

 naria rubra, Spergula arvensis, Papaver arge- 

 mone, P. hybridum, Thymus serpyllum, Rumex 

 acetosella, Acynos vulgaris, Trifolium arvense, 

 Lamium purpureum, abound. 



Loamy soils produce Anagallis arvensis, Sher- 

 ardia arvensis, Valerianella olitoria, Lithosper- 

 mum arvense, Lapsana communis, Sonchus ole- 

 raceus, Fumaria officinalis, Gnaphalium margra- 

 telia, Triticum repens, Chrysanthemum leucan- 

 themum. 



Gravelly and peaty, — In the former chiefly Poly- 

 gonum convolvulus, P. aviculare, Aira caryo- 

 phyllea, Agrostis vulgaris, Lolium perenne, 

 Papaver dubium ; and on the latter Vaccineum 

 (various species), Spergula subulata, Tormentilla 

 officinalis, Calluna vulgaris, Erica tetralix, Ga- 

 lium aparine, present themselves. 



Rumex acetosella indicates the presence of 

 iron, Equisetum arvense a cold and retentive 

 subsoil, Alchemilla aphanes is indicative of a 

 most unproductive soil; while Cirsium arvense 

 and Senecio Jacobea, although both affecting 

 light and strong loams, indicate in both cases a 

 fertile one, and the little Draba verna and Scle- 

 ranthus annuus are found on the most sterile of 

 all. 



This list might be greatly extended, but we 

 have confined it to such plants as are likely to 

 be met with on soils intended for gardening 

 operations. Stellaria media and Fumaria offici- 

 nalis are indicative of a rich condition of soil. 



Chemical analysis. — Most of the authorities 

 we have consulted seem to hold out little hope 

 that the majority of cultivators, in their present 

 state of chemical knowledge, can derive much 

 advantage from attempting to analyse soils 

 themselves, and therefore recommend the em- 

 ployment of professed chemists, who have both 

 the requisite conveniences and a thorough know- 

 ledge of the subject, founded on scientific prin- 

 ciples. 



The quantity of soil best adapted to a perfect 

 analysis is stated to be 400 grains ; it should be 

 collected in dry weather, and exposed to the 

 air till it becomes dry to the touch. Discretion 

 must be used in selecting specimens for exami- 

 nation, as soils differ much even within a very 

 limited space. It should therefore be taken 

 from different places, and from 2 to 3 inches 



below the surface. It is here that the first and 

 principal difficulty arises in the true analysis of 

 soils ; and if due caution be not exercised, the 

 chemical result may be as far from the truth, as 

 regards the whole field, as if we trusted to its 

 nature from examining the plants which grow 

 upon it. Soils, when collected for this purpose, 

 if not immediately submitted to the chemist, 

 should be kept in close-stopped phials until 

 wanted. 



All soils, as may be supposed, are variable in 

 composition: their nature is generally a good 

 deal dependent on the subsoil and the stony 

 matters beneath the siirface, many of which are 

 slowly decomposing or crumbling away, and 

 adding to the soil the substances of which they 

 consisted. 



We have already stated that a soil, to be use- 

 ful for the purpose of cultivation, consists of 

 silica, potash, soda, alumina, lime, magnesia, 

 oxide of iron, oxide of manganese, phosphoric 

 acid, sulphuric acid, chlorine, and organic matter. 

 We shall now glance at the relative importance 

 of these constituents to plants, and their amount 

 in the soil, upon the authority of Dr Henry 

 Madden of Brighton, as quoted in " The Book 

 of the Farm." 



" Silica. — This is the pure matter of sand, 

 and also constitutes on an average about 60 per 

 cent of the various clays, so that in a soil it 

 generally amounts to from 75 to 95 per cent. 

 In its uncombined state it has no direct influence 

 upon plants, beyond its mechanical action in 

 supporting the roots, &c. ; but as it possesses 

 the property of an acid, it unites with various 

 alkaline matters in the soil, and produces com- 

 pounds which are required in greater or less 

 quantity by every plant. The chief of these are 

 the silicates of potash and soda, by which ex- 

 pression is meant the compounds of silica, or 

 more properly silicic acid, with the alkalies 

 potass and soda. 



" Alumina. — This substance never exists pure 

 in soil. It is the characteristic ingredient of 

 clay, although it exists in that compound to the 

 extent of only 30 or 40 per cent. It exerts no 

 direct chemical influence on vegetation, and is 

 scarcely ever found in the ashes of plants. Its 

 chief value in soil, therefore, is owing to its 

 effects in rendering soil more retentive of mois- 

 ture. Its amount varies from | per cent to 13 

 per cent. 



" Oxide of iron. — There are two oxides of iron 

 found in soils — namely, the peroxide and pro- 

 toxide ; one of which, the protoxide, is fre- 

 quently very injurious to vegetation — indeed, so 

 much so, that \ per cent of a soluble salt of this 

 oxide is sufficient to render soil almost barren. 

 The peroxide, however, is often found in small 

 quantities in the ashes of plants. The two 

 oxides together constitute from \ to 10 per cent 

 of soil. The blue, yellow, red, and brown 

 colours of soil are more or less dependent upon 

 the presence of iron. 



" Oxide of manganese. — This oxide exists in 

 nearly all soils, and is occasionally found in 

 plants. It does not, however, appear to exert 

 any important influence either mechanically or 

 chemically. Its amount varies from a mere 



