ESTFLUENCE OF THE FOREST ON FLOODS. 229 



moisture to the mineral eartli below, and tlius is ready to receive 

 a new supply ; and, besides, the bed of leaves not yet converted 

 to mould takes up and retains a very considerable proportion of 

 snow-water as well as of rain. 



The stems of trees, too, and of underwood, the trunks and 

 stum]3s and roots of fallen timber, the mosses and fungi and the 

 numerous inequahties of the ground observed in all forests, oppose 

 a mechanical resistance to the flow of water over the sm-face, 

 which sensibly retards the rapidity of its descent down declivities, 

 and diverts and divides streams which may have already accumu- 

 lated from smaller threads of water.* 



* In a letter addressed to the Minister of Public Works, after the terrible in- 

 undations of 1857, the late Emperor of France thus happily expressed himself : 

 "Before we seek the remedy for an evil, we inquire into its cause. Whence 

 come the sudden floods of our rivers ? From the water which falls on the 

 mountains, not from that which falls on the plains. The waters which fall on 

 our fields produce but few rivulets, but those which fall on our roofs and aro 

 collected in the gutters, form small streams at once. Now, the roofs are 

 mountains — the gutters are valleys." 



"To continue the comparison," observes D'Hericourt, "roofs are smooth 

 and impermeable, and the rain-water pours rapidly off from their surfaces ; 

 but this rapidity of flow would be greatly diminished if the roofs were carpeted 

 with mosses and grasses ; more still, if they were covered with dry leaves, little 

 shrubs, strewn branches, and other impediments — in short, if they were wood- 

 ed." — Amlales ForestUres, Dec, 1857, p. 311. 



The mosses and fungi play a more important part in regulating the humid- 

 ity of the air and of the soil than writers on the forest have usually assigned to 

 them. They perish with the trees they grow on ; but, in many situations, 

 nature provides a compensation for the tree-mosses and fungi, in ground 

 species, which, on cold soils, especially those with a northern exposure, spring 

 up abundantly both before the woods are felled, and when the land is cleared 

 and employed for pasturage or is deserted. These humble plants discharge a 

 portion of the functions appropriated to the wood, and while they render the 

 soil of improved lands much less fit for agricultural use, they, at the same 

 time, prepare it for the growth of a new harvest of trees, when the infertility 

 they produce shall have driven man to abandon it and suffer it to relapse into 

 the hands of nature. 



In flourishing natural forests, when the ground is not too moist to admit of 

 a dense growth of trees, the soil is generally so thickly covered with leaves that 

 there is little room for ground mosses and mushrooms. In the more open arti- 

 ficial woods of Europe these forms of vegetation, as well as many more attract- 

 ive plants, are more frequent than in the native groves of America. See, on 

 cryptogamic and other wood plants, Rossmassler, Der Wald, pp. 33 et seq., 

 and on the importance of such vegetables in checking the flow of water, Men- 

 GOTTi, Idraulica Fisica e Sperimentale, chapters xvi. and xvii. No writer 



