122 APPLICATION OF PEINCIPLES. 



cause is suddenly withdrawn by the momentary supply 

 of water being cut oif by evaporation, and by filtration 

 through the bibulous substances of which soil usually 

 consists. Then again, the rapid evaporation from the 

 soil in dry weather has the effect of lowering the tem- 

 perature of the earth, and this has been before shown 

 to be injurious (p. 113) ; 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 little 

 while the effect of "puddling" the ground and render- 

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

 roots is impeded, whether it is communicated artifi- 

 cially, or by the fall of rain.* It is, therefore, doubtful 



* [No error is more common in this country than surface- 

 watering newly transplanted trees; and we do not hesitate to 

 aflSrm that full one half the failures, in our dry summers, arise 

 from this injudicious practice. By pouring "water daily on the 

 top of the ground, under a powerful sun and strong wind, the sur- 

 face becomes so hard that access of the air to the roots is almost 

 precluded ; and the water rarely penetrates more than a couple 

 of inches ; while the operator imagines he is supplying the thirsty 

 roots with abundant moisture, he is doing them an injury by the 

 application of a very transient stimulus, which is followed by an 

 increased sensibility to the drought In late spring planting, it is 

 always preferable to water abundantly in the hole, while planting 

 the tree, before filling in the upper layer of soil. This will in 

 most cases suffice, until the tree becomes sufficiently established 

 by the emission of new rootlets to support itself; and also serves 

 to ensure its growth by filling up all the small hollows around the 

 lesser fibres. In seasons of continued drought, when it becomes 

 absolutely necessary to water flagging trees, two or more inches 



