SUMMER TREATMENT OF GREEN-HOUSE PLANTS. 



157 



case out of fifty do the spongioles absorb 

 one single drop of the moisture so applied. 

 This argument bears more strongly upon 

 sandy soils, which contain but a small 

 quantity of organic matter ; and hence, a 

 proportionately small amount of water is 

 chemically combined. It is best retained 

 mechanically among the pores of the sur- 

 face earth, until it is carried off by evapo- 

 ration. 



When water is applied to the plants and 

 trees, growing in the open ground, it ought 

 to be done thoroughly, and done but sel- 

 dom ; and if a good soaking cannot be 

 given them, the better way will be to let 

 them alone. Stirring the soil somewhat 

 deeply will let the water more readily to 

 the roots ; and stirring the surface gently 

 the day after watering, will prevent the 

 moisture from being drawn off so rapidly 

 by the sun's rays. The roots will also be 

 kept cooler, because the rough surface will 

 present an impediment to the transmission 

 of the heat downwards. 



There is some difference of opinion 

 among practical men, regarding the proper 

 time for watering plants. Some prefer the 

 morning, others the evening, and both par- 

 ties present very plausible arguments in 

 their favor. But I think the great majority 

 of people, by a sort of general consent, ad- 

 here to the system of watering at night ; 

 without, however, having any very well 

 determined notions whether it is right or 

 wrong, — doing it just because everybody 

 else does it, — each person taking the ex- 

 ample of his neighbor as a very good rea- 

 son why he should do it himself. We 

 have, indeed, some reason to suppose that 

 evening watering is preferable to that of 

 the morning, because the atmosphere then 

 becomes moister. by the doscension of the 

 vapors which have been drawn up, and 

 suspended in the air by the heat of the 



sun. The moisture is thus received more 

 gradually into the system of the plants. 

 My own experience, however, has induced 

 me decidedly to prefer the morning water- 

 ing ; and I think I may say r that scientific 

 men are for the greater part in favor of 

 this method, especially in periods of long 

 continued drouth, in light, silicious or 

 sandy soils. 



One of the principal objections to water- 

 ing in the evening is cooling the surface 

 excessively', and chilling the roots of the 

 plants. Nothing is more injurious to ve- 

 getable, as well as to animal life, than rapid 

 changes of temperature. And this must 

 be produced by the application of water 

 50° or more below the temperature of the 

 earth in which the plants are growing. 

 The difference is sometimes much greater, 

 when no care is exercised in modifying 

 the temperature of both. In the moist 

 climate of northern Europe, and some other 

 parts of the globe, where the number of 

 rainy days exceeds dry ones, this circum- 

 stance has less influence on vegetation, 

 because the temperature of the surface soil 

 seldom exceeds the lower stratum of air. 

 But under our scorching sun, the fact is 

 different, and is perceptible to the most un- 

 observant individual, and the cause is ob- 

 vious ; for here the temperature of the soil 

 frequently rises from 10° to 20° above the 

 superincumbent atmosphere. The wilted 

 appearance of our vegetables, and the 

 stunted eTowth of our trees, is not owinsj 

 to the excessive heat of the atmosphere, 

 but rather the excessive heat of the soil, 

 and the absence of moisture ; and hence, 

 we need not exercise our energies in re- 

 ducing the temperature of the atmosphere 

 by evaporation from the soil, but rather in 

 reducing the temperature of the soil by the 

 absorption of moisture from the air and 

 otherwise. 



