30 



Mont., type of alkali soiP). Addition of sodium siilpliate, which is 

 itself so injurious in a pure solution, raises the limit for magnesium 

 sulphate three times, while the presence of calcium sulphate allows a 

 small proportion of the roots to barelj^ survive during twenty-four 

 hours in a solution of magnesium sulphate 480 times as concentrated 

 as that which, in pure solution, represents the limit of endurance. A 

 careful comparison was made between 0.3 and 0.4 normal solutions of 

 magnesium sulphate, both in the absence and the ijresence of an excess 

 of calcium sulphate, five individuals of Lu2:)inusalbus being cultivated 

 for 48 hours in each of the four solutions, 

 the results: 



The following table gives 



Table IV. — Magnesium sulphate with and icithout calcium sulphate. 



Solutions. 



Average 

 elongation 



of the 

 marked por- 

 tion of the 

 root. 



General condition of the roots. 



Magnesium sulphate (0.3 normal) 



Magnesium sulphate (0. 3 normal) + calcium 

 sulphate. 



Magnesium sulphate (0.4 normal ) 



Magnesium sulphate (0. 4 normal) + calcium 

 sulphate. 



Millirneters. 

 0.7 



10.: 



.3 

 13.0 



Extremely flaccid, and discolored 

 with brownish blotches; extreme- 

 ly plasmolyzed. 



Turgor normal; plasmolysis none; 

 but all roots quite badly discol- 

 ored/ 



About as in 0. 3 normal. 



Turgor normal; plasmolysis none; 

 all but one root quite badly dis- 

 colored. 



In both pure solutions the protoplasm of the nearly isodiametric 

 cells of the periblem was completely withdrawn from the cell wall and 

 collected with the nucleus in a compact mass near the center of the cell; 

 while in both solutions to which calcium sulphate had been added 

 no trace of plasmolyzing action could be detected in the cells of the 

 periblem, the protoplasm being closely applied to the wall, with large 

 vacuoles in the older cells, and the nucleus usually i)eripheral. Pre- 

 cautions were taken while preparing the sections to keep the tissues 

 immersed in the culture solution, and the absence of i:)lasmolysis in 

 the roots taken from the solutions containing calcium sulphate is 

 sufficient evidence that the pure solutions had produced this effect 

 during the period of culture rather than after withdrawal.^ 



^See Whitney and Means, Bui. 14, Div. Soils, U. S. Department of Agriculture 

 (1898), and Cameron, Bui. 17, p. 32, Div, Soils, U. S. Department of Agriculture 

 (1901). 



^Wolf's observation (see- footnote, p. 40) that both Ca (NOg),^ and Mg (N03)2 

 are readily absorbed by plant roots when mixed together, while neither is readily 

 absorbed from a pure solution, renders it highly probable that in this case of a 

 mixture of MgSO^ and CaSO^ it is the rapid endosmosis of the salts into the cells 

 of the plant roots which prevents plasmolysis of the latter. In short this mixture 

 is to be compared with those substances described by Overton [Vierteljahrsschr. 

 Naturf. Gessells ch. Zurich 40, 1 (1895)] which produce only transient plasmolysis, 

 owing to their more or less rapid passage through the ectoplasm into the cell sap. 

 As determined by De Vries [Jahrb. fiir wiss. Botanik. 14, 537 (1884)], a 1.8 per 

 cent solution of magnesium sulphate (which would correspond to our 0.3 normal 



