SCR 



535 



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ted the too free circulation of the air; i den and Norway remaining covered 

 and when in immediate contact with with snow, whilst England is some 20^, 



the polished bark of the peach, pcrlKi|)s 

 another law of cooling came into ope- 

 ration. The law is, that polished sur- 

 faces radiate heat slowest. Thus, if 

 two glass bottles, equal in size and 

 thickness of glass, and of the same 

 shape, be tilled with warm water, and 

 one of the bottles be covered with an 

 envelope of fine muslin, this bottle will 

 give out heat to the surrounding air 

 with much greater rapidity than the 

 other bottle; so that, in a given time, 

 the bottle with the envelope will be 

 found colder than the one which has 

 no covering. 



Screens, such as the preceding, or 

 the slighter agents, sprays of ever- 



or more, warmer; and an upper cur- 

 rent of warm air is consequently flow- 

 ing hence to those countries, whilst a 

 cold under current is rushing hither to 

 supply its place. This wind, and its 

 consequent cold weather, is so regular 

 in its appearance, that in Ilampsliirc, 

 and some other parts of England, the 

 peasantry speak of it as the black thorn 

 winter, that bush being in blossom dur- 

 ing a part of its continuance. — Princ. 

 ofGnrd. 



Not only are screens required for 

 out-door plants, but for those under 

 glass ; and Mr. Paxtoji is quite right in 

 saying, that " one of the tilings vvhich 

 should be constantly borne in mind, 



greens, placed before the branches ofj and more especially in the forcing sea- 

 wall-trees or other plants, as already son, is the most etTectual means of keep- 

 noticed, operate beneficially in another ing up the requisite temperature in the 

 way, checking the rapid passage of the , hot-houses with least fuel ; and that, in 

 air over them: such passage is detri- ' all cases where practicable, the use of 

 mental in proportion to its rapidity, for | external coverings, if properly used, 

 the more rapid it is, the greater is the \ will render strong fires in a great niea- 

 amount of evaporation, and, conse- ! sure unnecessary. Some coverings are 

 quently, of cold produced. Mr. Daniell used at Chatsworth constantly at night, 

 says, that " a surface which exhales v.hich makes frcmi ten to titteen degrees 

 one hundred parts of moisture when ; dilference in the temperatures of the 



the air is calm, exhales one hundred 

 and twenty-five parts when exposed to 

 a moderate breeze, and one hundred 

 and fifty parts when the wind is high." 

 During all high winds, but especially 

 when blowing from points varying be- 

 tween the east and the south, for they 

 are the driest in this country, the gar- 



if)uses where they are appiiod, and to 

 maintain which, without them, would 

 consume three times the quantity of 

 fuel now necessary." — Gard. Chron. 



P'or wall-trees, now that glass is be- 

 come so ninch cheaper, the best of all 

 screens may be employed, viz., glazed 

 frames, of a length extending from the 



dener will always find shelter is bene- i coping of the wall, to the surface of 

 ficial to his plants, whether in blossom, the soil, about two feet from the stems 

 or with fruit in its first stages of growth, i of the trees. 



for these winds cause an evaporation 

 much exceeding in amount the supply 

 of moisture afforded by the roots. 



In March, such shelters are much 

 required, for the winds are then violent 

 and dry even to a proverb ; but it is 

 during the days of its successor, April, 

 that sets in the only periodical wind 

 known in this island. It comes intcr- 

 mittingly, and with a variable force 

 from poi[its ranging from east to north- 

 east, and is one of the most blight- 

 ing winds we have. It continues until 

 about the end of the second week in 

 May, though often until its close ; and 



SCREW I'INR. Pandanus. 



SCREW TREE. Hdicteres. 



SCROPHULARIA. Figwort. Seven 

 species. Hardy herbaceous perennials. 

 S. vcrnalis, a biennial. Seeds. Light 

 soil, and a moist situation. 



SC RU B B Y O A K . Loph ira nfricam . 



SCURVY GRASS. Cochlear ia offici- 

 nalis. " This vegetable grows sfionta- 

 ncously on the sea shores of England, 

 and is also found in the interior. It is 

 used like the Cress, and occasionally 

 mixed with corn salad. 



" Sow in autumn and manage as di- 

 rected for winter spinach; it is used 



it is a good plan to have the tree, dur- during the winter and spring." — R. Reg 

 ing the whole period, by day as well To obtain Seed. — A few plants must 

 as by night, protected. This periodical be left ungathered from in the spring, 

 wind is occasioned, probably, by Swe-' They will run up to flower about May, 



