270 



The Dictionary of Gardening, 



Kafnia — continued. 



cuneate, lanceolate, linear-lanceolate, or lineav-filiform, sub- 

 obtuse or acute. Bianchlets angular, h. 1ft. to 14ft. 1816. 

 Sul]-.-;hvul>. SVN. It. filifalia. 

 R, elliptlca (ollijiticleaveil). jl.., peduncles axillary, one- 

 tlowereil, with a pair uf It'.-ify bracts under the tiower. June. 

 I, 2in. to 3in. long, broadly obovate, elliptical, oblong, or ovate- 

 lanceolate, acute or obtuse and niucronate ; upper ones narrow 

 and more lanceolate, all narrowed at base. Brandies angular. 

 h. 1ft. to 3ft. 1819. .Shrub. 



R. filifolia (thread-leaved). A synonym of Ji. aiiindata. 



R. trillora (three-fiowered).* jl, keel about twice as long- as 

 the calyx tube ; peduncles axillary, one to three together, 

 leafless, or branched and leaf-bearing. June. I. liin. to 3in. 

 long, roundish-oliovate, elliptical (»r ovate-laiu^eolate, acute or 

 nuiL-ronillate, obtuse at base, liranches angular or two-edged. 

 />. 2ft. to 1ft. 1784. Shrub. (B. M. 482, under name of 

 Cnfalaria Irijtora.) 



KAGGED ROBIN. See Lychnis Plos-cucnli. 



RAGWEED, or RAGWORT. See Senecio 

 Jacobsa. 



RAGWORT. See Othonna. 



RAIIiIiARDIA (named in honour of A. M. L. Raillard, 

 an officer in the French Marine service). Okd. Compositw. 

 A gemis comprising- nine species of greenliouso shrubs, 

 confined to the Sandwich Islands. Flowor-heads yellow, 

 rayless, mediocre or small, racemose or corymbose at the 

 apices of the branches ; involacre cylindrical or narrow- 

 campanulate, with one series of connate or at length 

 free bracts ; receptacle small, convex or sub-conical, 

 naked or setose-fimbrilliferous ; achenes narrow, glabrous, 

 or slightly pilose. Leaves opposite, ternately whorled, 

 or altern.ate, sessile, entire, coriaceous, at length shining. 

 For culture of the only species introduced — now pro- 

 bably lost to gardens — see Senecio. 



R, ciliolata (fringed-leaved). jl.-lmuls five to eight, clustered in 

 a paniculate corymb ; achenes sub-tetragonal, attenuated at 

 base. July. I. ternately whorled, lanceolate, glabrous on both 

 sides, rather more than iin. long, shortly ciliated on the margins. 

 Branches velvety-pubescent, h. 2ft. 1865. (B. M. 5517.) 



RAIN*. A familiar example of the origin and nature 

 of Eain is seen in the formation of a miniature shower, 

 when steam escapes from a steam-engine into the air. 

 When water is heated, it becomes an invisible vapour ; 

 and this rises, and mixes with the air, if the air is 

 warm. When the warm air, full of water in this state, 

 mixes with cold air, or touches any cold object, the 

 vapour returns to the state of water ; but, for a time, 

 it remains in the form of very small particles, like fine 

 dust — so light, that they can still float in the air. In 

 this state, they form clouds when high above the earth, 

 or mist when lying close to the eatth. Among moun- 

 tains, clouds and mists are often seen to be directly 

 continuous. But mists often cling to the mountain-tops 

 while the sky is nearly cloudless. This is owing to the 

 rocks and soil being colder than the air, and causing 

 the vapour to become visible as mist, by cooling the air 

 near them below the temperature at which the water can 

 remain vapour. As the wind carries the mist from the 

 mountain into the warmer air around, it resumes the 

 form of vapour, and becomes invisible ; but new mist is 

 formed, and supplies the place of that carried away, so 

 that the mist seems to remain unchanged on the peaks for 

 hours. Clouds form and disappear in the sky according 

 as the air filled with vapour meets colder or warmer 

 winds. When the minute drops of water that form clouds 

 are very crowded, they join together, and form drops, 

 too large to be supported in the air. These then fall as 

 Eain. Sometimes, a cloud will be seen raining high up 

 in the sky, though Eain does not reach the ground. This 

 happens when the Eain has to fall through a layer of 

 warm, dry air, in which it is all turned into vapour 

 again. Light Eain sometimes falls out of a sky cloudless 

 or nearly so ; but this is a rare occurrence. The greater 

 amount of rainfall during the night is due to the cooling 

 of the air when the sun's heat is withdrawn. The vapour 



Rain — continued. 

 forms drops of water, and falls as Eain. The sources 

 of the vapour in the air are various. Much of it is 

 given off by growing plants, and a little by animals. 

 More is taken up by w-arm, dry winds blowing over the 

 surface of the land, with its marshes, rivers, and lakes ; 

 but most of all is absorbed by the winds in passing over 

 the oceans, such .as the Atlantic Ocean. Such winds are 

 saturated, or nearly so ; that is, they carry away as much 

 vapour as they can dissolve at the temperature they had 

 while passing over the water. If this is higher th m 

 that of the land at which they first arrive, they will give 

 up, as Eain, the vapour that no longer can be dissolved 

 when the temperature falls. Hence, countries near oceans 

 receive more Rain than those at a distance from them 

 in the middle of continents. Mountainous countries near 

 the sea are especially rainy, since air becomes colder 

 the higher it rises along the slopes, and a very great 

 part of the vapour is thus lost. For the reasons just 

 stated, as well as from local peculiarities of situation, 

 the frequency and amount of the rainfall varies widely 

 in different localities, and at different seasons. The total 

 amount of Eain that falls in any given time is measured 

 by means of instruments {see Rain-gauge). Careful 

 observations have been carried on in many countries, and 

 in many localities, for a consideraV>lo number of years, 

 as to the total amount of Eain that falls during the year, 

 as well as during the various periods of the year, in 

 each locality. The amount is expressed in the number 

 of inches in dejjth that the Eain would reach in any given 

 time, if it could all be confined to the exact area on 

 which it has fallen. 



It has been found that, in some countries in the 

 tropics, e.g., in Upper Egypt and the Sahara Desert, 

 and on part of the coast of Pern, little Eain, if any, 

 falls. On the other hand, the heaviest recorded rainfall 

 occurs among mountain ranges in the neighbourhood of 

 tropical oceans. Thus, in the Himalaya Mountains, 

 about 100 miles from Calcutta, a rainfall of about 

 .5"24in., or about i-tft., has been observed within a year. 

 In the British Islands, the rainfall is considerably 

 greater on the west side than on the cast, the winds 

 from the Atlantic Ocean losing much of their vapour 

 among the mountains. The heaviest rainfall in Britain 

 is recorded from the Cumberland mountains, near Kes- 

 wick, where over 150iu., or I'J^ft., of Eain has been 

 collected in a year. Along our western coasts, the 

 average aniuial rainfall varies from about 3Gin. to GtJin., 

 and on the eastern .side of our islands, from about 20in. 

 to 30in. 



But the actual rainfall does not bear any definite 

 relation to the number of rainy days in a year, for often 

 the heaviest fall is met with in districts where it is 

 almost limited to certain seasons. When much Eain 

 falls in a limited time, the greater part of it necessarily 

 flows off the surface of the ground, and it is apt to 

 carry away the fertile soil, and to cause disastrous 

 floods. Where, on the other hand, the period during 

 which it falls is more prolonged, the Eain sinks into 

 the soil, and supplies the underground reservoirs of 

 springs. 



In passing through the atmosphere, the rain becomes 

 of the same tempei'ature, aud, as this in summer is 

 almost always higher than that of the soil, the latter 

 becomes warmed, and the plants in it are stimulated to 

 more active growth. Moreover, the rain-water has 

 oxygen, and, it may be, also minute traces of ammonia 

 and of nitric acid, obtained from the atmosphere, dis- 

 solved freely in it, .and these also are beneficial, as 

 food, to the roots of plants. It is unnecessary to dilate 

 on the importance of a good supply of water in the 

 soil, insured to plants by regular Eains. 



Eain-water is very generally preferred for watering 

 plants in pots, and it has the great advantage " over 



