44 



SOIL CONDITIONS AND PLANT GROWTH 



Those receiving only small amounts of water, have small 

 glaucous leaves and tend early to form seed. As the water 

 supply increases, the root system increases rapidly both in 

 extent and in fineness ; with further supplies, the leaves be- 

 come successively larger and greener in colour, ripening be- 

 comes delayed, but the root system becomes restricted and 

 alters in character, finally consisting of a few stout roots only. 

 Von Seelhorst (257^) has made quantitative determinations of 

 the proportions of root system to entire plant under conditions 

 of varying water supply. 



Table VII. — Growth of Barley with Varying Supply of Water. 

 Hellriegel (130a). 



Amount of water 



Dry matter in grain, gms. 



Dry matter in straw, gms. 



I grain weighed, mgms. — 



100 represents the amount of water required to saturate the sand. 



These morphological differences are accompanied by dif- 

 ferences in chemical composition of the plant. Even the seed 

 is affected, a phenomenon which does not usually occur when 

 other factors such as supplies of plant nutrients are varied. 

 Thus the composition of the wheat grain is hardly affected by 

 manuring, but it is profoundly altered by variations in water 

 supply^ (Shutt, 265). Other instances have been recorded 



^ C. H. Bailey, Minnesota Expt. Sta. Bull., 131, 1913, has drawn up the 

 following table, showing the protein content of the wheat and flour of the 

 hard spring wheat grown in sixteen counties in Minnesota (ist April to ist 

 September, 1911). 



Rainfall, 



Between 12-13 ins. 



14-15 .. 

 16-17 „ 



18-19 „ 

 20-21 ,, 

 22-24 ,, 



Stewart and Hirst, Utah Expt. Sta. Bull., 125, p. 145, obtained the follow- 

 ing results at Utah, showing the effects of irrigation. 



