37 



as fast as transmitted. It is therefore not long before the 

 feeding-bed of the roots under such surface-crust is far too 

 dry for their proper function, the growth of root-hairs 

 (eases, and the trees begin to show signs of flagging. 

 Unfortunately the habit of many growers is to endeavour to- 

 set things right solely by running in an abundant irrigation 

 and practically flooding the root-bed. As the water srets 

 slowly away by percolation, most of it is evaporated from 

 the surface and the crust reproduced, with the inevitable 

 result of the same capillary rising of the very water just 

 administered and its dissipation into the air. There is 

 therefore a pernicious alternation of a fast and a feast 

 forced upon the roots. The true remedy consists in inter- 

 posing a loose, powdery or fibrous stratum several inches 

 thick between the layers of soil in which the roots live and 

 perform their functions and the external air, ever greedy 

 of moisture. 



41. Now there are two ways of doing this. One is of 

 limited application, although it answers perfectly. It con- 

 sists in covering the soil round a tree or plant with a layer 

 of short broken straw or waste stable fodder. Gardeners 

 know this plan of old, and call it " mulching." Under it, 

 however sun-smitten and dry it may become, the soil is 

 always more or less moist, never cakes into a crust, and 

 never robs the water content of the root-stratum. In fact 

 loss of moisture through the capillarity of the interstices 

 between the particles of the soil is completely stopped by 

 these tubes (for such they practically are), never reaching 

 the free air at. all. Some will take it for granted, off-hand, 

 that the preservative effect of the straw mulch is due only 

 to its shadowing the soil from the rays of the sun, ; but 

 careful experiments have completely disproved such sup- 

 position. About one-fourth only of the total effect is due 

 to the mulch preventing insolation ; the rest is due to its 

 stopping the capillary withdrawal of the soil's moisture- 

 content at a point short of the evaporating surface. If 

 then it were possible to mulch completely the surface of an 

 orchard or vineyard in this manner, there would rarely, if 

 ever, be so complete a drying out of the feeding ground of 

 the roots as to cause flagging and wilting of the foliage. 

 But the method is in a general way only applicable on the 



