172 WATBEING IN THE OtBN AIE. 



operation is usually performed in hot dry weather, and must 

 necessarily be hmited in its effects ; it can have httle if any 

 influence upon the atmosphere : then, the parched air robs the 

 leaves rapidly of their moisture, so long as the latter is 

 abundant ; the roots are suddenly and violently excited, and 

 after a short time the exciting cause is withdrawn, by the 

 momentary supply of water being cut off by evaporation, and 

 by filtration through the bibulous substances of which soil 

 usually consists. Then, again, the rapid evaporation from 

 the soU in dry weather has the effect of lowering the 

 temperature of the earth, and this has been before shown 

 to be injurious ; such a lowering, from such a cause, does not 

 take place when plants are refreshed by showers, because at 

 that time the dampness of the air prevents evaporation from 

 the soil, just as it prevents perspiration from the leaves. 

 Moreover, in stiff soils, the dashing of water upon the surface 

 has after a httle while the effect of "puddling" the ground and 

 rendering it impervious, so that the descent of water to the 

 roots is impeded, whether it is communicated artificially or by 

 the faU of rain. It is, therefore, doubtful whether artificial 

 watering of plants in the open air is advantageous, unless in 

 particular cases ; and most assuredly, if it is done at all, it 

 ought to be much more copious than is usual. It is chiefly in 

 the case of annual crops that watering artificially is really 

 important; and with them, if any means of occasionally 

 deluging ground can be devised by means of sluices or other- 

 wise, in the same way as water-meadows, it may be expected to 

 be the most advantageous. 



The best gardeners employ overhead watering in the open air only 

 in cases of absolute necessity. A curious case is recorded of a garden 

 in a sandy soil at Tonbridge, in Surrey, which, through the hot and 

 dry summer of 1842, remained in the most luxuriant beauty without 

 receiving any assistance from watering. In this case the gardener 

 stated that the garden in question was some eight years previously 

 partly pond, and partly a sandy bank. The former was filled up witiL 

 earth ; the latter was removed to the depth of three feet. A compost 

 prepared of sandy loam, decayed vegetable mould, silver sand, and 

 lime, well mixed and seasoned, was substituted, to the depth of three 

 feet; and, under these circumstances, although not even a thunder 



