GECXLOOY. 251 



throwing out suckers from the roots, and since the grass is continually 

 cropped close and tramped down by cattle, the former vegetation of 

 the prairies has gradually given way to softer and shorter grasses, the 

 rank prairie ancf barren grasses dying out. At many points also tim- 

 ber is encroaching spontaneously upon laud formerly occupied by tall 

 grasses ; while, on the contrary, old forests yield to the axe and the 

 ploughshare. The effect of these changes upon the climate, especially 

 in decreasing the humidity of the country, must be powerful, and may 

 be compared to the change of sensation which we experience, on a 

 clear summer evening, in coming from a sheltered damp creek bottom 

 to the airy top of a dry hill. The effect is similar to that produced in 

 other countries by the clearing of extensive forests. The growth of 

 dense tall grasses, of which untold generations have died and rotted 

 upon the same spot, not only protects the soil from the warming rays 

 of the sun and thus checks evaporation, but it actually increases the 

 precipitation of moisture, especially in the form of dew, by the low de- 

 gree of temperature consequent upon the humidity of the surface and 

 upon the powerful radiation of heat from the spears and leaves of the 

 grass waving in the night air, which, as can be easily proved by ex- 

 periment, grow much colder than the bare soil. The grasses also check 

 the surface drainage effectually. With their disappearance, the 

 above effects cease, the soil becomes more exposed to the direct rays 

 of the sun and to the drying breezes, while the succeeding growth 

 does not favor the precipitation of dew nearly as much as the grass. 

 The natural impediments to the speedy abduction of the falling rains 

 are also lessened to a considerable degree, and thus the soil is rendered 

 dryer. The artificial works of drainage, and even the cuts and ruts of 

 the roads do their share also. The breaking up of the sward and deep 

 cultivation of the soil facilitate the sinking of the water, and expose a 

 greater surface of soil to the desiccating influence of the sun and winds. 

 Every old settler can bear witness to the remarkable and rapid change 

 in the conditions of moisture of the prairies, which is also manifested 

 by the gradual failing of the wells at numerous points. It is a com- 

 mon observation, that they must be du<* much deeper now than for- 

 merly in the same vicinity. The healthiness of the country has there- 

 by improved, and the farmer is enabled to plant much earlier, and at 

 points which were formerly too wet ; his loss by the freezing out of the 

 winter crops is much reduced. The droughts in summer and fall are 

 perhaps also more severe at present, but an advantage can seldom be 

 gained without some sacrifice, and a remedy is accessible if only we 

 will apply it. This is "thorough cultivation and underdraining." 

 Where these are practised, the roots are enabled to strike deeper, be- 

 yond the direct influence of the sun's rays ; a much larger quantity of 

 nourishment is presented to them ; the humidity of the soil is equal- 

 ized ; its absorbing power for moisture and gases is vastly increased ; 

 and the growth of the plants is consequently much invigorated and 

 placed beyond the reach of sudden changes of the weather. 



THE DISTRIBUTION OF ARCTIC PLANTS. 



Dr. Hooker, of the Kew Botanic Gardens, has published a memoir 

 on this subject in the Linnean Society's Transactions, which will be 

 fully appreciated by geographical botanists. The Arctic flora forms a 



