174 VEGETABLE MOISTURE. 



vegetables, gets moist without the falling of any 

 rain, or the formation of any dew. Growing vegeta- 

 bles give out a great deal of moisture to the atmo- 

 sphere, because their absorbent vessels take in much 

 more than is wanted for the addition of matter made to 

 the plants in the process of growing. Water, or the 

 component parts of water, decomposed and assimi- 

 lated when in the aerial or gaseous state, no doubt 

 go to the actual substance of the plant ; but much 

 of the water passes through the plant, as the mere 

 vehicle of that part of the food which forms the 

 nourishment : and that water is again given out to 

 the air by evaporation. When the air is very warm 

 and dry, more water is evaporated than is consistent 

 with the healthy state of the plant : and in conse- 

 quence the leaves become soft and feeble, and the 

 whole plant droops. If the languishing is not very 

 great, the plants are again recovered by the night, 

 and next morning finds them able to bear the sun of 

 a new day ; but if it be too severe or too long con- 

 tinued, the delicate vessels of the leaves are shriv- 

 elled, the juices do not circulate, the light does not 

 perform its proper functions, and the leaves lose 

 their greenness and wither. 



But when a cloud comes under the circumstances 

 just noticed, the evaporation from the plant is sus- 

 pended ; and the moisture which would have been 

 dissipated in a more drying state of the air remains 

 and refreshes the leaves. In the banks of rivulets 

 and the sides of drains there -are often little trick- 

 lings of water, so small in quantity, that the dry air 

 and the heated bank draw it into vapour almost be- 

 fore it reaches the surface; and the places seem 

 absolutely dry. But when the evaporation is sus- 

 pended by the cloud which cools the ascending air 

 and sends it down again, so that it continues taking 

 moisture alternately from the earth and cloud, those 

 tricklings appear ; and fresh moisture is apparent on 

 the earth before any begins to fall in visible rain 

 from the sky. 



