lOO 



Journal of Agricultural Research 



Vol. Ill, No. 1 



ally diminish the evaporation there. In comparing the three zones, how- 

 ever, the evaporation in the Hudsonian and Canadian zones was found 



to be, respectively, 13 and 35.6 percent 

 less than that in the Transition zone. 

 Owing to the relative great evaporation 

 in the latter region, light showers, espe- 

 cially those which fall early in the day 

 and are succeeded by a clear sky, are 

 soon evaporated and so are of little 

 value to plant growth. During a period 

 of drought, other things being equal, a 

 plant could not live nearly as long in 

 the lower as in the higher elevations, on 

 account of the excessive transpiration 

 in the former locality. 



To sum up the conditions peculiar to 

 the Hudsonian zone as compared with 

 the lower grazing type, the temperature 

 is lower, the precipitation heavier, and 

 the transpiration less. It is therefore 

 easy to see that the relatively slow- 

 growing and warmth-requiring vegeta- 

 tion in the lower lands could not thrive 

 in the cooler and shorter growing season 

 typical of the Hudsonian zone. Hence, 

 only the most plastic and adaptable 

 species of the Transition zone occur in 

 the Hudsonian, and then only on the 

 warmest and most exposed south slopes. 



LIFE HISTORY OF THE FORAGE 

 PLANTS 



The growth requirements of range 

 plants can best be determined by a 

 study of individual species and the 

 factors with which they have to con- 

 tend from the time that they begin 

 growth in the spring through the 

 various stages of development to 

 seed maturity, and then on to the 

 permanent establishment and seed- 

 bearing stage of the vegetation i)ro- 

 duced from seed of the original plants. The essential features of this 

 almost double life cycle are: (i) Inception of growth, (2) flower-stalk 



