22 The Winds; Agenc;/ of Water in Vegetation. 



88. The Winds. In considering atmospheric agencies, the drying 

 effects of the winds should be noticed, as liable to be greatly in- 

 creased by the clearing of lands, and to be lessened by planting. 

 These plantations, in order to serve most effectually as wind-breaks, 

 should extend across the direction from whence the prevailing winds 

 blow. In the states west of the Mississippi, the dry and warm 

 winds, most injurious to vegetation, come from the south-west, and 

 it is against these that we should chiefly guard. 



89. The winter storms of greatest violence, known in the North- 

 western States as " blizzards," come from the north-west. There can 

 be no doubt but that their local effects may be reduced, and to some 

 extent their occurrence diminished by the plantations of groves of 

 trees. 



90. In some countries exposed to prevailing ocean winds, there 

 will be ample rainfall under any condition, and woodlands can have 

 but little effect; for, whether present or absent, the humid air from 

 the ocean will precipitate its moisture when it comes over the laud. 

 In Norway, the amount of rain on the western coast is over 80 inches 

 a year. In Great Britain and Ireland, and on the western coast of 

 France, the rains will be abundant from these causes, as they will 

 always be along our Pacific coast. But these ocean winds in passing 

 over mountain ranges must necessarily be cooled down to a degree 

 much below the dew point, and become dry by being thus depleted 

 of their moisture as they pass inland. 



The Agency of Water in Vegetation. 



91. Whether in solid form, as snow or ice, or as a liquid, supplied 

 by rains, dews, or irrigation, or as a vapor, water acts an essen- 

 tial part in vegetation, and is necessary for the existence of all vege- 

 table life. For best effect it should be seasonable and sufficient, but 

 not in excess. 



92. As a general rule, seeds will not germinate under water, but 

 in some trees the roots will bear submergence for a considerable time. 

 The wood of trees thus exposed is often softer and more spongy than 

 it would have been if grown on dryer ground. Generally, however, 

 a sustained overflow of the surface causes the death of the trees 

 whose roots are thus covered, and " beaver meadows " are thus 

 caused. 



93. The Snow is a slow conductor of radiant heat, while it allows 



