682 



niSTORY OF THE VEGETABLE KINGDOiU. 



formed ; but occasionally' the watch-glass cracks 

 on cooling. Sometimes the watch-glass becomes 

 displaced aftei- a time ; but this inconvenience is 

 of little moment, as an adroit person may easily 

 restore it in two minutes. AVhere the mouth of 

 the jar is larger, the most effectual plan, and at 

 the same time the easiest, is to tie one layer of 

 sheet caoutchouc over it in the usual way for 

 anatomical preparations. The caoutchouc should 

 be stretched over the jar, but not strongly, by 

 one, or still better by two persons, while another 

 secures round the neck two or three folds of stout 

 twine as a temporary ligature. A thinner twine 

 is then drawn steadily and tightly round three 

 or four times above the former, care being taken 

 not to cut the caoutchouc. 



Solution of salt is comparatively inapplicable, 

 however, where the friiit is very pulpy, — in such 

 fruits, for example, as solanum lycopersicum, or 

 lemons and oranges ; because the fruit shrivels 

 by exosmosis of its fluids. Diluted pyroligne- 

 ous acetic acid, diluted to the density of 1008, 

 sometimes answers well in such circumstances; 

 but after a few years the texture of the speci- 

 mens becomes so pulpy and brittle, as not to 

 admit of their being handled, and most colours 

 are in no long time more or less altered. Spirit, 

 which is most generally used, speedily renders 

 all colours alike brown ; but is probablj' better 

 for delicate specimens which may be subjected 

 to minute dissection. 



PLANT CASE FOR GROWING PLANTS 

 IN AN ISOLATED ATMOSPHERE. 



This apparatus was originally invented by Mr 

 Ward of Wellclose Square, London, and pro- 

 mises to be a useful and elegant portable con- 

 servatory to the lovers of plants residing in a 

 crowded city. 



In consequence of the vitiated atmosphere of 

 large cities, even the most common plants and 

 flowers wither and die away within a very short 

 period. Drs Turner and Christison have ascer- 

 tained, that it is not simply to the diffusion of 

 smoke through the air, but to the presence of 

 sulphurous acid gas generated in the combustion 

 of coal, that the mischief is to be ascribed. When 

 added to common air, even in the proportion of 

 one ten-thousandth part, this gas was found sensi- 

 bly to affect the leaves of growing plants in ten 

 or twelve hours, and killed them in forty-eight 

 hours or less. The effects of hy drochlori or muri- 

 atic acid gas were still more powerful, it being 

 found that the tenth part of a cubic inch in 

 20,000 volumes of air manifested its action in a 

 few hours, and entirely destroyed the plant in 

 two days. Both these gases acted on the leaves, 

 affecting more or less their colour, and withering 



and crisping their texture, so that a gentle touch 

 caused their separation from tlie foot stalk, and 

 both exerted this injurious operation when pre- 

 sent in such minute proportions as to be wliolly 

 inappreciable by the animal senses. In this way 

 vegetation is affected in the vicinity of some manu- 

 factories, around a circumference of fully one-third 

 of a mile. After having suffered considerable 

 injury from these acid gases, the plants, if re- 

 moved in time, will recover, but witli the loss 

 of the foliage. Hence, in vegetation carried on 

 in a vitiated atmosphere, the plants are rarely 

 instantaneously destroyed, but only blighted for 

 the season. In the following spring, vegetation 

 again commences with its accustomed luxuri- 

 ance ; and as in many situations there is at 

 that season, and throughout the summer, a dimi- 

 nution in the number of coal fires, there will be 

 a proportionate decrease in the quantity of dele- 

 terious gases, and consequently less injury will 

 be done to plants. In winter too, when the 

 atmosphere is at its worst, deciduous plants are 

 protected from its noxious operation, by a sus- 

 pension of their vegetative powers while ever- 

 greens are, on the other hand, constantly exposed 

 to its action. Accordingly, in London and other 

 large towns, especially in manufacturing cities, 

 vegetation is almost entirely destroyed. It was 

 in order to protect his favourite flowers from the 

 baneful influence of the city atmosphere, that 

 Mr Ward contrived to inclose them in a limited 

 atmosphere, and he found that plants continued 

 to gTOw in this confined condition as vigorously 

 and as freshly as in the free air of the country. 

 The late Mr Ellis of Edinburgh thus describes 

 a plant case constructed for him after the model 

 of Mr Ward's: 



It is composed of three parts; the stand, tlie 

 box, and the glass roof or cover. The stand is 

 one foot ten inches in height, tlie box eight and 

 a half inches, and the cover one foot seven and 

 a lialf inches, making the total height four feet 

 two inches. The stand on which the box rests 

 is made of mahogany, and supported on four 

 legs furnished with movable castors. The box 

 contains the soil, and is made of well seasoned 

 mahogany, previously steeped for a fortnight in 

 Kyan's preservative composition. It is a pai'al- 

 lelogram, three feet long, and one and a half feet 

 broad ; its sides are one and a half inches thick, 

 mitred and dove-tailed at the corners ; the bot- 

 tom of the box is of Honduras mahogany, one 

 inch thick, and is formed of numerous small 

 pieces, framed and flush pannelled, and so ar- 

 ranged as best to resist the yielding of tlie wood 

 in consequence of the mass of moist earth which 

 it has to bear. To give it greater strcngtli, two 

 cross or tie pieces stretch from side to side, and 

 are dove- tailed into the sides. They are placed 

 at equal distances from the two ends, and thus 

 divide the box into three compartments, but as 



