SNA 



[741] 



SOI 



SNAILS. See SLUGS. 



SNAIL FLOWER. Phase'olus caraca'lla. 



SNAKE GOURD. Zrichosa'nthes. 



SNAKE ROOT. Aristolo'chia serpenta'ria. 



SNAKE WOOD. Brosimum AubletiL 



SNAPDRAGON. Antirrhi'num and Sile'ne 

 ttntirrhi'na. 



SNEEZEWORT. Achille'a Pta'rmica. 



SNOW is one of the gardener's best 

 shelters, and should never be removed 

 from his out-door crops. It prevents 

 heat from radiating from them ; protects 

 them from freezing, drying blasts, and, 

 being a bad conductor of heat, thus pre- 

 vents its escape from them. We have 

 never known the surface of the earth, 

 below a covering of snow, colder than 

 32, even when the temperature of the 

 air above has been 28. 



SNOWBALL-TREE. Vibu'rnum o'pulus. 



SNOWBERRY. Chioco'cca. 



SNOWDROP. Ane'mone sylve'stris and 

 Gala'nthus. 



SNOWDROP-TREE. Hale'sia. 



SNOWFLAKE. Leuco'jum. 



SOAP-BOILER'S ASHES. See ASHES. 



SOAPWORT. Sapona'ria. 



SOBRA'LIA. (Named after F. M. Sobral, 

 a Spanish botanist. Nat. ord., Orchids 

 0rchidacese]. Linn., 2Q-Gynandria 1- 

 Monandria.) 



Stove orchids, grown in pots. See ORCHIDS. 

 5. chlora'ntha (yellow-flowered). Yellow. June 

 Brazil. 



deco'ra (comely). Various. July. Guatimala 



1836. 



dicho'toma (two-ranked). Rose, purple. March 



Peru. 



lilia'strum (lily-flowered). White. July. Guiana. 



1840. 



macra'ntha (large-flowered). 6. Crimson. 



September. Guatimala. 1842. 

 splefndens (splendid). 3. Crimson. Sep- 

 tember. Guatimala. 1846. 



se'ssilis (stalkless). Pink. December. Peru. 



1840. 



viola'cea (violet). Violet, white. July. Merida. 



SOIL. However varying in the propor- 

 tions, yet every soil is composed of silica, 

 alumina, lime, magnesia, oxide of iron, 

 salts, and animal and vegetable remains. 

 A fertile soil is one which contains such 

 a proportion of decomposing matter and 

 of moisture as to keep the crop growing 

 upon it always supplied with food in a 

 state fit for the roots to absorb, yet not 

 so superabundantly as to render the 

 plants too luxuriant, if the object in 

 view is the production of seed ; but for 

 the production of those plants whose 

 foliage is the part in request, as spinach, 

 or of edible bulbous roots, as onions, 



which have a small expanse of leaves, so 

 as to be almost entirely dependent upon 

 the soil for nourishment, there can 

 scarcely be an excess of decomposed 

 matter presented to their roots. 



A subsoil of gravel, mixed with clay, is 

 the best, if not abounding in oxide of 

 iron; for clay alone retains the moisture 

 on the arable surface in too great an 

 excess ; and sand or chalk, on the con- 

 trary, carries it away too rapidly. It is, 

 however, evident, that to insure these 

 desiderata in any soil, at all seasons, is 

 impossible ; and it is manifest that a soil 

 that would do so in one climate would 

 fail in another, if the mean annual 

 temperature of them should differ, as 

 well as the amount in inches of rain 

 which falls during the same period. Thus, 

 in the western parts of England, more 

 than twice as much rain occurs as in the 

 most eastern counties, or in the propor- 

 tion of forty -two to nineteen. A soil in 

 the east of England, for any given crop, 

 therefore, may be richer and more tena- 

 cious than the soil required for it on the 

 western coast. 



Alumina (clay) imparts tenacity to a 

 soil when applied; silica (sand) dimi- 

 nishes that power ; whilst chalk and lime 

 have an intermediate effect. They render 

 heavy soils more friable, light soils more 

 retentive. These simple facts are impor- 

 tant ; two neighbouring gardens, by an 

 interchange of soils, being of ten rendered 

 fertile, which before were in the extremes 

 of tenacity and porosity. 



In affording warmth to plants, the 

 earth is of considerable importance, and 

 the power of accumulating and retaining 

 heat varies as much in soils as the 

 proportions of their constituents. Sir 

 Humphry Davy found that a rich black 

 mould, containing one-fourth of vegetable 

 matter, had its temperature increased, in 

 an hour, from 65 to 88 by exposure to 

 the sunshine, whilst a chalk soil was 

 heated only to 69 under similar circum- 

 stances. But the first, when removed 

 into the shade, cooled in half an hour 

 15; whereas the latter lost only 4 C . 

 This explains why the crops on light- 

 coloured, tenacious soils are in general 

 so much more backward in spring, but 

 are retained longer in verdure, during 

 autumn, than those on black, light soils , 

 the latter attain a genial warmth the 

 more readily, but part from it with equal 



