52 MINNESOTA I50TANICAL STUDIES. 



p. 142), but usually there was no response unless the solution was 

 made strong^er, in whicii case the stimulus was a negative one. The 

 criteria for comparing weak and strong acid solutions shows that 

 tiie latter did not always accelerate transpiration more forcibly than 

 the weaker solutions, contrary to the belief of most investigators. 

 I'luctuating variations in transpiration were observed from time to 

 time, some individuals being absolutely out of proportion to the be- 

 havior of a large number of similar plants which were tested in the 

 same way and under the same conditions. Where extreme discrep- 

 ancies of this sort occurred, the plants were discarded. 



It must be borne in mind that in most experimentation of this 

 kind, there will occur unexplainable variations, and the true re- 

 sults must be attained from the summation of a great number of ex- 

 periments. The above discrepancies might not have occurred had 

 the number of plants used been larger. 



Relation of Soil Textures and Some Soil Types to Tran- 

 spiration. 



It was deemed of sufficient importance, in connection with the 

 other lines of investigation, to grow plants in various soil textures 

 and in some of the common soil types and test the response of 

 transpiration to them. 



Wheat plants were used throughout, four being grown in each 

 pot. A Minnesota variety was selected, known as ''Minnesota No. 

 66." Pure quartz sand was used for the work on textures. The 

 .soil particles were sifted through a series of screens, the size of the 

 meshes being as follows : 



Series I, 10 per square inch; Series II, 15; Series III, 20; Series 

 IV, 40; Series V, 60, and Series VI, 80 per square inch. 



Three pots in each series ^ were run both in the original and in 

 the check. For all series the initial moisture content of the soils 

 was about twelve per cent. For both this experiment and that of 

 'Soil Types" the transpiration was determined daily for a period of 

 nine days. The pots of all series stood side by side in the plant 

 house, where they were subjected to exactly the sam.e changes in 

 temperature, light, humidity, and air currents. Only two plants 

 were run in each type because of the great amount of labor re- 

 quired in separating them. 



At the end of the experiment both series were photographed. The 



* ICxceptlon : Series V and VI. 



