NOURISHMENT OF PL.VNTS THROUGH LEAVES. 181 



276. Other experiments show the remarkable influence of 

 dew, in supplying nourishment to plants. Two similar leaves of 

 the Plantago lanceolata (Ribwort Plantain), equally faded, and 

 each weighing 8 grains, were compared ; one having its footstalk 

 immersed in water, and the other being exposed to dew. On 

 the following morning, the first had gained but one grain, whilst 

 the second (after the adherent moisture was wiped off) was found 

 to have gained a grain and a half. A similar experiment was 

 then tried upon two leaves of Verbascum (Mullein), each of 

 which weighed 13 grains in the first instance. The one whose 

 footstalk was immersed in water gained 2^ grains; whilst the 

 other gained 4 grains. Many other experiments of a similar 

 kind might be related; but these are sufficient to show, that 

 leaves whose tissue has been deprived of fluid, have the power 

 of replacing it by absorption from water placed in contact with 

 them, or from a moist atmosphere. This power is probably 

 exercised, however, in the majority of plants, only when their 

 roots cannot from any cause obtain for them an adequate supply; 

 and at other times the leaves are organs of exhalation only. 



277. The influence of dew and of a moist atmosphere in 

 maintaining vegetation, is often very remarkable in tropical 

 islands, where no rain falls for months together, and where the 

 soil is so parched by the burning sun, as scarcely to yield a par- 

 ticle of fluid to the plants growing upon it. The proximity of 

 the sea occasions the atmosphere of these islands to contain a 

 large quantity of vapour, which, when the temperature of the 

 soil falls at night, is deposited as an abundant dew ; and, incon- 

 sequence, they exhibit a luxuriant vegetation, tinder circumstances 

 which would cause an inland country to appear completely 

 parched. In the year 1840, the preservation of the young corn 

 during the hot and dry month of April, in many parts of 

 England, was owing to the heavy dews. In consequence of the 

 wetness of the preceding autumn and winter, very little grain 

 had been put into the ground before February ; and, as there 

 was little rain from that time, the surface of the ground was not 

 sufficiently moist, to cause the rapid germination and growth of 

 the young plants. Towards the middle of April the sun began 



