18 WHEAT EESISTANCE TO TOXIC SALTS. 



mal solutions stock solutions Avere made up by dilution, and Avere 

 kept for use as recpiired. T\w solutions actually used in the experi- 

 ments were made from the stock solutions by diluting Avith distilled 

 Avater, It might seem at first that two successive dilutions would 

 permit of an error. This, however, has been avoided in the case 

 of chlorids and carbonates by titrating each stock solution before 

 using. The concentration of the solutions of sulphates was fre- 

 quently verified by analysis in the Bureau of Soils. Sodium car- 

 bonate and sodium bicarbonate were both titrated against N/20 

 hydrogen potassium sulphate, using methyl orange as an indicator. 

 In the case of the bicarbonate solutions it Avas necessary to charge 

 them Avith an excess of carbon dioxid to preA^ent their becoming 

 alkaline. The nonalkalinity of the bicarbonate solutions Avas often 

 tested by the addition of a dro]) of alcoholic phenolphthalein, Avhich 

 Avould indicate the presence of alkalis by forming the Aveli-knoAvn red 

 color. Sodium chlorid and magnesium chlorid Avere titrated against 

 N/10 of sih^er nitrate. WheneA^er, upon titration, any stock solu- 

 tion Avas found to be either too dilute or too concentrated, it Avas cor- 

 rected by the addition of more of the normal solution or by further 

 dilution Avith distilled Avater. The Avater used in these exjDeriments 

 Avas distilled in the Laboratory of Plant Pathology, and near the 

 close of the Avork Avas found by analysis in the Bureau of Chemistry 

 to contain some slight amount of a toxic substance. That this Avas 

 for all practical purposes neutralized and played no part in the 

 toxic action of the solutions used is demonstrated in the fuller dis- 

 cussion of this point on page 39 of this paper. 



All seeds for these experiments Avere germinated in sphagnum moss. 

 After being finely broken uj) the moss was placed in a bucket and 

 kept sufficiently moist for seed germination. It Avas found that the 

 seedlings Avere injured if kept too moist, the roots shoAving an en- 

 largement at the apex, developing into a very blunt tip, and Avhen 

 aifected in this Avay they usually stopped groAving and ncAv roots Avere 

 put forth. The initial radicle Avas more easily aifected in this Avay. 

 Only seedlings having healthy and vigorous rootlets Avere used in the 

 experiments. The seeds Avere first soaked in hydrant Avater from four 

 to six hours before being placed in the sphagnum moss. After about 

 three days in the temperature of an ordinary room they Avere ready 

 for use. They Avere most easily manipulated when the radicles Avere 

 from three to four centimeters long. The root itself might Avell be 

 longer, but the apical bud appears almost at the same time as the root, 

 and Avhen more than one or tAvo centimeters long interferes with easy 

 adjustment in the beakers. It was sometimes necessary to pinch off 

 the ends of the leaA^es, a practice which in ho Avay interfered with the 

 development of the rootlets. AMien the radicles had reached the 

 length mentioned aboA^e, the seedlings Avere taken out of the sphag- 



