THE GROWTH OF WHEAT SEEDLINGS AS AFFECTED 

 BY ACID OR ALKALINE CONDITIONS. 



INTRODUCTION. 



The following physiological study on the effect of the reaction of 

 the culture medium on the growth of wheat seedlings and particu- 

 larly on the development of the root was undertaken primarily to 

 determine whether or not the results obtained in practical agriculture 

 can be explained in the laboratory from a purely scientific standpoint. 



A few years ago Director Thorne, of the Ohio experiment station, 

 called the attention of one of the authors to peculiar conditions exist- 

 ing on certain of his fertilizer experiment plots, to which potassium 

 chlorid and potassium sulphate had been applied annually for the 

 past 12 years. These plots had become so acid that it was found 

 impossible to grow clover on them. Liming one-half of each plot 

 had restored that half to almost its original fertility. This acidity, 

 he said, was due to the selective action of the root, doubtless a correct 

 explanation which will be considered in detail later. 



There seems to be a natural tendency for all soils to become acid 

 under continuous culture, due chiefly to one of two processes. The 

 primary cause of this acidity is the decay of organic matter, leaves, 

 stems, etc., which during decomposition develop acid-reacting bodies. 

 If this process is allowed to continue, the reaction will ultimately 

 become alkaline, but under soil conditions, especially if the aeration 

 is poor and the water level high, decay is apt to be checked^ leaving 

 the soil in a characteristic acid condition. This phase of soil acidity, 

 which will not be considered in this bulletin, has been studied exten- 

 sively during the past few years, particularly by the Rhode Island and 

 Ohio experiment stations, and by Mr. Frederick V. Coville 1 in his 

 elaborate investigations on the blueberry. Peat bogs furnish an 

 exaggerated case of acidity, due to organic matter. The secondary 

 cause of soil acidity is the subject of the investigation herein reported. 



*U. S. Dept. Agr., Bureau of Plant Industry Bui. 193. 



