36 



NEW YOliK STATE MUSEUM 



For oats there was needed in 1870. according to Risler, a 

 quantity of water 250 times the weight of dry material con- 

 tained in the crop. In 1871 clover transpired 263 units of 

 water to produce one unit of dry substance, and English ray- 

 grass 545 units of water for one unit of hay containing 15 per 

 cent of water. For this last the quantity of water corresponds 

 to 0.276 inch in depth per day. 



Risler observed, furthermore. That following rains or wet- 

 tings transpiration of plants increases, gradually diminishing 

 in proportion as dryness increases, other conditions remaining 

 equal. When the w T ater given off by the leaves is less than that 

 taken up by the roots, growth is active, while under the contrary 

 condition, plants wither. 



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In a general way, the consumption of water by plants is 

 more regular in clay soils than in sandy. Hellriegel states that 

 in a sandy soil plants begin to suffer from drouth when the soil 

 does not contain more than 2.5 per cent moisture. Risler finds 

 that the approximate limit for clay soils is 10 per cent, although 

 in clay soil, part of the water escapes absorption by the roots. 



Taking as a basis the observations made on the crops raised 

 at Caleves, Risler expresses the mean daily consumption of 

 water as a depth on the cropped area as follows: 



Inches. 



Meadow grass requires from 0.134 to 0.267 



Oats require from . 141 to . 193 



Indian corn requires from . 110 to . 157 



Clover requires from . 140 to 



Wheat requires from . 106 to . 110 



Rye requires from 0.091 to 



Potatoes require from . 038 to . 055 



Vineyards require from . 035 to . 031 



Oak trees require from . 038 to . 035 



Fir trees require from . 020 to . 043 



Risler determined the consumption of water on a meadow of 

 one hectare (2.47 acres) of very thickly turfed English ray-grass 

 as 281 millimeters (11.06 inches), amounting to a daily depth of 

 0.267 inch. This consumption applies to a meadow well provided 

 with water during the w r armest season of the year. The ex- 

 periments showed that on cloudy days evaporation was reduced 

 to about one fourth of the mean, that is, to 0.069 inch per day. 



In Switzerland the fields begin to grow green the latter part 

 of March, and the bay harvest occurs in June; hence, the growth 

 of the plant takes place in April and May> The point is brought 



