20 WHEAT RESISTANCE TO TOXIC SALTS. 



A word as to the conditions of illumination and temperature during 

 the experiments will not he out of place at this point. When in 

 solutions the roots were exposed to the liaht (hu-inu- the day. When 

 in the salt solutions during the first 24 hours they were kept on a 

 shelf in the rear of a room with northern exposure only. When in 

 hydrant Avater during the second 24 hours they were kept on a table 

 at the window, under a moderately strong light. Preliminary experi- 

 ments were made when commencing the Avork Avith lupines, which 

 showed that the strength of the light, at least within the limits in- 

 voh^ed in these experiments, had no influence on the growth of the 

 roots. Of three series of cultures, all in a solution of the same salt 

 at the same concentration, one was placed in total darkness, another 

 in subdued light, and a third in bright light. Otherwise they were 

 under the same conditions. The elongation of the roots was meas- 

 ured at the end of 24 hours and there AAas no appreciable dilferen'ce 

 in the three sets of cultures. 



It was impossible to keep a uniform temperature in the laboratory 

 during the Avinter months, though this factor did not vary enough 

 in either direction to cause any injury in germination or to the roots 

 in the solution. A thermograph Avas kept running in the room, and 

 a review of the records shoAvs no temperature below 18° or above 

 30° C. The average temperature during the experiments was about 

 23° C. When making the experiments Avith illumination referred to 

 above, similar ones Avere made to determine the influence of tempera- 

 ture upon the roots. The three different series of cultures (all in 

 the same salt solution, at the same concentration) Avere exposed for 

 24 hours to temperatures of 10°, 20°, and 30° C, respectively. 

 Results shoAved that the roots that had been exposed to a temperature 

 of 20° and 30° C. shoAved about the same elongation, Avhile the elonga- 

 tion in a temperature of 10° C. Avas somcAvhat less. 



All solutions Avere made Avith water distilled from ordinary hydrant 

 Avater. The receiver of the still is a porcelain tub and has been used 

 for several years in the Laboratory of Plant Pathology of the Bureau 

 of Plant Industry. At times the distilled Avater may have contained 

 some slight traces of ammonia and doubtless some other imi)urities. 

 An analysis of the Avater Avas made in the Bureau of Chemistry, and it 

 was found to contain, in parts per million — 



Zinc Ti'ace. 



Free ammonia 0. V2o 



Albuminoids • ^^^ 



Nitrates ^one- 



Nitrites Faint traces. 



Total solids (consisting of calcium, sodium, carbonates,, sul- 

 phates, and chlorids) '•'•4 



A further discussion of the water used will be found on page 39. 



