AN ENCYCLOPEDIA OF HORTICULTURE. 



Sobralia continued. 



S. suaveolens (sweet-smelling). /. yellowish-white, richly per- 

 fumed ; lip white, brown on the disk of the front lobe, the keels 

 yellow. Central America, 1878. This species is very similar in 

 habit to S. decora. 



S. violacea (violet), fl. pale violet, larger than those of 

 S. decora ; lip convolute, not unlike that of a Cattleya ; bracts 

 imbricated, somewhat leafy. July. I. hard, lanceolate, deeply 

 plicate; sheaths slightly waited. 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. I. lanceolate, acuminate, 

 plaited, the sheaths dotted with brown. Native country un- 

 known. (Gn. xxii. 366 ; W. O. A. vi. 250.) 



SOCRATEA (named after the philosopher Socrates, 

 the greatest of the Greeks). ORD. Palmai. 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, cnneate-flabellate, deeply laciniate, the laciniae 

 narrow, sinuate-toothed. Only one species calls for men- 

 tion here. Its aerial roots are studded with small 

 spines, used by the Indians as a Cassava grater. For 

 culture, see Iriartea. 



S. exorhiza (rooting outwards). Zanona Palm, fl., spathes five 

 or six, deciduous ; spadix 14ft. long, spreading when flowering, 

 pendulous in fruit. Jr. yellowish or yellowish-green, scarcely 

 fleshy, ovate-elliptic, eight to twelve lines !ong. I. 12ft to 20ft. 

 long ; pinnae oblique, sub-trapezoid, sinuate-toothed, flat ; 

 petioles cylindrical, convolute at base. Trunk 60ft to 100ft. 

 high. Aerial roots eight to twenty or more, emerging 6ft. from 

 the ground. Guiana, Amazons River, 1849. SYN. Iriartea 

 exorhiza. 



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 Holciis. 



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 ilb., 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. IIL 



Soil continued. 



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 or 

 lb., 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 is 

 thus determined. Each is then examined with a good 

 lens, and the proportions of pure quartz sand (silica), 

 mica, yolcanio 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 chemical 

 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 ascertain 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. 



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, 



3M 



