Naturally other conditions also enter into the question; thus, for ex- 

 ample, color also becomes a considerable quantity when the soil is sufficiently 

 damp and has a favorable mechanical form. The darker the earth the more 

 plant growth is favored. Mixed soils give better results than clear peat, 

 sand or loamy soils. 



a. Too Steep Slopes. 



Soil surfaces of more than 15° to 20° inclination in a small area must be 

 used so far as possible for meadow and grazing land if gardening and vine- 

 yards do not warrant expensive terracing. If the inclination of any surface 

 approximates 45° it'is urgently advisable to retain all existing vegetation and 

 to attempt forestration or to complete it with suitable planting. 



This utilization of surfaces, at such an inclination, is not only the best 

 method but also the best protection of the lower adjacent cultivated land. 

 Such steep slopes, only found in mountains, rarely have a deep loam even 

 when covered with forests. Under such conditions only the thickly matted 

 root systems of the trees can keep off the destructive gullying and washings 

 after heavy rains and from storms after continued drought if the soil con- 

 tains much sand. The moss cushions of forests retain moisture necessary 

 for the further disintegration of the rocks and increase the tendency to 

 form springs ; which benefit is felt only on the plains. It is easy to 

 observe, that the pith has become eccentric when the trees are growing on 

 steep declivities. Mer\ studying firs and spruces of the Vosges, ob- 

 served that, in trees growing on steep cliffs, the annual rings are more strong- 

 ly developed on the side toward the upper incline than on that toward the 

 declivity. This occurs especially at the base of the trunk. On cliffs lying 

 toward the north and east, the firs and spruces were not only taller and 

 stronger but the annual rings of the individual trees varied more markedly 

 in the same points of the compass. If the trees have to grow twisted, the 

 annual rings show a stronger development on the convex side at the points 

 of twisting. 



Unfortunately our cultivated lands show the sad results of the deforesta- 

 tion of steep slopes. The forest was here the product of consecutive pro- 

 cesses many hundred years old, which probably began with the colonization 

 of lichen encrustations on the naked rock. Through the retention of the 

 products of weathering, these and gradually larger plants began to form a 

 surface soil and with their decomposed bodies furnished the first humus 

 substances, making the soil better and better adapted for the growth of 

 higher plants. Once robbed of this covering of vegetation, the bursts of rain 

 sweep the surface soil downward, exposing the stony sub-soil on the heights 

 and filling up the tilled land on the plains. With greater deforestation of 

 the mountain, the water supply of the mountain streams becomes the more 

 irregular and, with more frequent spring floods in the lowlands, covers them 

 with sand; also in dry sum.mers the streams are without water. 



1 Mer, Des causes qui produisent I'excentricite de la moelle dans les 

 Compt. Rend. Vol. CVl, 1888, p. 313. 



