VEGETABLE MOISTURE. 175 



that the surface of the earth in many places, and 

 especially that of the green vegetables, gets moist 

 without the falling of any rain, or the formation 

 of any dew. Growing vegetables give out a great 

 deal of moisture to the atmosphere, 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 assi- 

 milated 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 evapo- 

 rated than is consistent with the healthy state of 

 the plant ; and in consequence 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 continued, the delicate 

 vessels of the leaves are shrivelled, the juices do 

 not circulate, the light does not perform its pro- 

 per 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 

 suspended; 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 tricklings of water, so small in quantity, that 

 the dry air and the heated bank draw it into va- 



