240 CONDITIONS OF GROWTH. 



phere is slight, and the soil becomes dry, and the sub- 

 soil is porous, the turf of our fields and pastures suffers 

 from drought, and scarcely a year passes over us when 

 this does not happen. 



A writer in the Journal of the fioyal Agricultural 

 Society, after many careful observations, comes to the 

 conclusion, First, That the growth of grass is always 

 proportionate to the heat of the air, if a sufficiency of 

 moisture be present in the atmosphere. Second, That 

 in the climate of England the moisture present is rarely 

 sufficient to allow the temperature to have full effect 

 when that temperature exceeds 56° ; but that, if moisture 

 be artificially supplied, as by irrigation, to catch-water 

 meadows, that then vegetation will still proceed in pro- 

 portion to the heat. Third, That when the temperature 

 of the air is between 36° and 41°, the grass will only 

 vegetate with a fifth part of the force that it will when 

 the temperature is 56°. Thus the land that will keep 

 ten sheep per acre, in the latter case, will only keep two 

 in the former. That from 41° to 46° its growth is two- 

 fifths, or double that of its growth when the tempera- 

 ture is under 41°, and it will then keep four sheep 

 instead of two. Again, from 46° to 50°, its growth will 

 rise to seven-tenths, or it will keep on the same ground 

 from five to seven sheep ; and from 50° to 56°, it gene- 

 rally — unless assisted by an artificial addition of moist- 

 ure — arrives at its maximum; but if the month of 

 June be very moist, it will continue to grow with an 

 increase of force up to 60°. 



Our climate is very different from that of England. 

 The evaporation from the soil is ordinarily very much 

 more rapid, and the actual amount of moisture in the 

 air is greater, since it is well established that the evap- 

 oration is in proportion to the height of the tempera- 

 ture and the extent of water or land surface ; that in 



