17 



cient amount, decolorized the tissues of the apical portion of the 

 root. This lost its normal brilliant white appearance^ and assumed 

 a lurid-whitish color. In the case of sodium carbonate (Xa2C03) 

 and of sodium bicarbonate (XaHCOg) there occurred a marked clear- 

 ing of the tissues similar to that produced by the hydrates of potas- 

 sium and sodium, the root tips becoming nearl}- transparent. This 

 change is completed long before any loss of turgor is apparent. Mag- 

 nesium salts (chloride and sulphate) discolored the surface of the 

 roots, producing brownish spots which gradually spread over the 

 whole surface.^ The difference in character of physiological effect 

 produced by salts of the same acid in the case of sodium on the one 

 hand, and of magnesium on the other, is very great when gauged by 

 these external appearances. 



Another effect produced by some of these salts is an irregular 

 enlargement of a i^ortion of the root. This is verj' marked in the 

 case of calcium chloride, in a solution of 0.3 normal or thereabouts. 

 The root just above the tip develops a fusiform swelling of which the 

 greatest transverse diameter (2 to 3 mm.) lies 5 to 10 mm. from the 

 apex of the root. A less marked formation of this sort is sometimes 

 produced by magnesium chloride, and even by other salts. ^ 



It is well to emphasize once more the fact that the death of the tip 

 of the primary root, and not that of the plant as a whole or even of 

 the entire root, was taken in these experiments as the indicator of the 

 toxic action of solutions. The condition of the distal 10 to 20 mm. 



1 The ■• shining white opaque appearance which is characteristic of all healthy 

 roots and which is due to air contained in the intercellular spaces." (Sachs, Land- 

 wirthsch. Versuchsst.. 1, 216: Gesarnmelte Abhandl.. 1,427). 



'Mettenius [quoted by Wolf in Landw. Versuchsst., 7, 202, (1865)] found that 

 these spots, which appear on the roots of both the bean and maize when placed 

 in solutions of magnesium salts, are due to a coagulation of the contents of the 

 epidermal cells, which he did not, however, further describe. Wolf remarks that 

 they do not appear upon plant roots in magnesium salt solutions if a salt of potas- 

 sium, ammonium, or calcium be present. 



-Sachs . Arb. hot. Inst. Wiirzburg. 1, 411. 412: Gesammelte Abhandl., 2, 800) 

 describes swellings of apparently similar character which developed upon roots 

 grown in moist air and watered at long intervals. Wolf [Landw. Versuchsst., 6, 

 218 (1864)] found that a concentrated solution of potassium sulphate acted in the 

 same manner. '-The root tips soon swell in the solution: the form of the root 

 finally resembles that of the root of a tuber-bearing plant. Such swellings arise 

 in particular abundance where lateral roots will break through." The action of a 

 one- fourth per cent solution of potassium nitrate upon roots of Lujjiiius albus as 

 described by True [Ann. of Botany, 9, 374 (1895 )] is exactly similar to that of cal- 

 cium chloride. '• Swellings appeared near the tips and the ends tapered suddenly 

 to sharp points. On the other hand, the growth in thickness was much greater 

 than normal, the radicles above the swellings reaching the size of large radicles 

 of Viciafaba of the same length.'" 



8287— No. 71—02 2 * 



