AN ENCYCLOPADIA 
7 
OF HORTICULTURE. 
Sobralia—continued. 
S. suaveolens (sweet-smelling). fl. yellowish-white, richly per- 
fumed ; lip white, brown on the disk of the front lobe, the keels 
ellow. Central America, 1878. This species is very similar in 
abit to S. decora. 
S. violacea (violet). jl. pale violet, larger than those of 
S. decora; lip convolute, not unlike that of a Cattleya; bracts 
imbricated, somewhat leafy. July. l. hard, lanceolate, deeply 
plicate ; sheaths slightly warted. New Grenada. Plant larger 
than S. decora. There is a variety having white flowers, with a 
yellow disk to the lip. 
S. xantholeuca (yellowish-white). fl. large and handsome, de- 
flexed ; sepals and petals pale yellow, the former oblong-lanceo- 
late, the latter broader and wavy at the edges ; lip longer, deeper 
yellow, much frilled, emarginate. J. lanceolate, acuminate, 
plaited, the sheaths dotted with brown. Npe puny un- 
Known. (Gn. xxii. 366; W. O. A. vi. 250.) - 7, farcouate-? 
SOCRATEA (named after the philosopher Socrates, 
the greatest of the Greeks). ORD. Palme. A small 
genus (three to five species) of stove, unarmed palms, 
natives of North -Brazil and Columbia. Spathes five to 
eight, deciduous, the upper ones complete; spadices 
solitary, horn-like and recurved before flowering. Fruit 
ellipsoid or oblong-obovoid, one or rarely two-seeded. 
Leaves few, terminal, equally pinnatisect; segments 
oblique, cuneate-flabellate, deeply laciniate, the laciniæ 
narrow, sinuate-toothed. Only one species calls for men- 
tion here. Its aérial roots are studded with small 
spines, used by the Indians as a Cassava grater. For 
culture, see Iriartea. ; 
S. exorhiza (rooting outwards). Zanona Palm.` fi., spathes five 
or six, deciduous ; spadix l4ft. long, spreading when fiovorug, 
pendulous in fruit. fr. yellowish or yellowish-green, scarcely 
fleshy, ovate-elliptic, eight to twelve lines Jong. l. 12ft. to 20ft. 
long; pinne oblique, sub-trapezoid, sinuate-toothed, flat; 
petioles cylindrical, convolute at base. Trunk 60ft to 100ft. 
high. Aérial roots eight to twenty or more, emerging 6ft. from 
the ground. Guiana, Amazons River, 1849. Syn. Iriartea 
exorhiza, 3 
SODA. A substance composed of the alkaline metal 
Sodium, combined with Oxygen, together with a certain 
amount of water, called Water of Hydration. Sodium is 
one of the most widely-diffused elements; and its nu- 
merous compounds are almost all readily soluble in water. 
It is very difficult to get entirely clear of the element, 
even in the chemical laboratory, and it is impossible to 
do so in soils: hence, plants are constantly supplied 
with it in solution from the soil, and it is found in the 
ashes of all plants. Experimental cultivation of plants 
from which it is, to the utmost, withheld, proves that it 
is not indispensable to any plant; though it has been 
asserted that Wheat, Oats, and Barley require an ap- 
preciable trace of Sodium to allow them to form perfect 
seeds. It has also been stated, as a result of experi- 
mental cultivation, that Sodium may, in part, function- 
ally replace Potassium in plants; but there seems reason 
to believe that Sodium produces very little, if any, 
effect on the health of plants, though indispensable in 
the nourishment of animals, including man. 
SODIUM CHLORIDE. See Salt. 
SOFT GRASS. See Holcus. 
SOIL. The comparatively soft and loose upper layer 
of the earth’s crust, upon which plants depend for their 
nourishment. The various kinds of Soils, and their modes 
of origin, will be found described below. Soils should be 
carefully examined as regards their composition and 
physical properties, in order to ascertain their capabilities 
for cultivation, the kinds of plants for which they are 
naturally best fitted, and the means by which they can 
be rendered more fertile. 
ANALysis. Soils may be examined in the following 
Way, as regards their general composition; and much 
valuable information can be obtained from such an 
analysis: The Soil is first thoroughly dried at 212deg. 
Fahr., and a given weight, say lb., is boiled in distilled 
water till the particles of which it is made up fall 
thoroughly apart. The substances in the soil that are 
soluble in pure water will be dissolved in this way; and 
Vol. III. 
Po 
Soil—contin 
the solution is carefully filtered through paper into a 
vessel, and kept for chemical analysis. The solid residue 
is carefully washed twice or thrice with distilled water, 
on a filter, to remove the whole of the soluble substances, 
and the washings are added to the solution. The residue 
is then thoroughly dried at 212deg. Fahr., and weighed; 
and the loss, as compared with the previous weight of | 
4lb., gives the amount of substances in the soil that are 
soluble in pure water. The solid material is then again 
washed, and the water is poured off, carrying with it 
the lighter particles. This is repeated till only the 
sand and gravel are left behind: these are dried and 
separated, by sifting through gauze. The washings, also, 
are collected and dried. The gravel, sand, and fine 
particles, which form the clay or mud of soils, are 
weighed separately, and the relative weight of each 
thus determined. Each is then examined with a good 
lens, and the proportions of pure quartz sand (silica), 
mica, volcanic rocks, limestone, or other minerals, are 
noted. This examination is facilitated if a little Hydro- 
chloric Acid (Spirit of Salt) is poured over the material 
under examination ; since quartz sand remains unchanged, © 
limestone is dissolved with the formation of bubbles of 
Carbonic Acid gas, ironstone is slowly dissolved, and the 
acid turns brown, and gives the very characteristic test _ 
for iron by turning blue when a solution of Prussiate of 
Potash is mixed with it. Other minerals in Soils give | 
less conspicuous results with the acid. The mical 
analysis of the portion soluble in water, and the com- _ 
plete analysis of the solid residue, require a considerable — 
knowledge of chemistry for the attainment of success, 
and should be entrusted to a professional analyst. : 
The amount of organic matter, i.e., remains of 
animals and of plants, in Soils, very greatly affects 
their value. The fresh Soil must be thoroughly dried, 
as already stated, to drive off the water as completely 
as possible. A given weight of it is then burned in a 
platinum dish, over a lamp, in the open air; and the 
burning is continued till all the blackness is got rid of, — 
i.e. till the Carbon is entirely burned away, The 
residue is then carefully weighed again, and the loss of 
weight represents the amount of organic matter de- 
stroyed. It is desirable to artain the conditions in — 
which the latter is present in the fresh Soil; but exact 
analysis demands more experience of chemical manipula- 
tion than is usually met with, except among chemists. 
Organic matter is usually present as Humic and Ulmic 
Acids (along with small quantities of some other organic 
acids), and insoluble vegetable matter, including often a 
good deal of tannin. Nitrates, also, are formed from _ 
organic remains. j ce 
Those who desire fuller details on the methods of 
analysis, will find them in most works on Agricultural 
Chemistry, such as Johnston’s ‘Analysis of Soils,” or 
Johnston and Cameron’s “Elements of Agricultural 
Chemistry and Geology.” 
PHYSICAL Properties. Not less valuable than the 
knowledge of the chemical composition of Soils, is that 
of certain properties grouped under the term heading 
this paragraph. Of these, the chief are the capacity for 
absorbing and retaining water, various chemical com- 
pounds, and heat; the density and power of cohesion of 
the particles of Soil, and the mode of shrinkage in dry 
weather. These vary greatly, according to the com- 
position of the Soil; but their general characters may 
now be indicated. 
Absorption and Retention of Water. This is a quality 
of great importance in fitting the Soil to supply the 
moisture required by plants. Soils absorb rain; though 
when the rainfall is very heavy, they cannot absorb more 
than a part, and the rest flows off the surface into 
streams. The capacity for absorption of rain-water, and 
for keeping it stored within reach of the roots of plants, 
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