TUEGIDITY 65 



Another manner of carrying out the direct test is to place 

 cells in the solution to be tested and, after sufficient time has 

 elapsed, to treat them with a reagent which will penetrate 

 and also give a visible reaction with the substance to be 

 tested. Thus, if penetration took place in the first solution 

 a microchemical test for the solute should be obtained within 

 the vacuole. In this way diphenylamin was first used by 

 Molisch^ to detect KNO3 in plant cells. With this reagent 

 a nitrate is indicated by the appearance of a blue color. It 

 appears from the work of Molisch, Wieler, De Vries, and 

 Janse, in which this method was used, that plant protoplasm is 

 very generally penetrated by KNO3 in dilute solution. In a 

 similar manner tests have been made with Pehling's solution, 

 which prove the penetration of glucose. 



Janse ' showed in this manner that Spirogyra protoplasts 

 are penetrated by KNO3. Wieler' worked with entire 

 plants of the angiosperm group and obtained similar results. 

 By means of diphenylamin and sulphuric acid he was able to 

 demonstrate that NO3 ions penetrate the protoplasts of seed- 

 ling beans, sunflowers, etc. By platinum chlorid he also 

 demonstrated the penetration of K ions. Stems placed in a 

 sugar solution formed starch, while a control without sugar 

 failed to do so. It made no difference whether cane sugar 

 or glucose were used. This proves the power of these sugars 

 to penetrate the protoplasts in stems. The last-named 

 author also presents evidence that the roots of seedlings of 

 Vicia faba are able to absorb glucose from a solution. Of 



1 H. M01.ISCH, "Ueber den mikrochemischen Nachweiss von Nitraten nnd 

 Nitriten in der FSanze mittelst Diphenylamin oder Bnicin," Ber, d. deutsch. bot 

 Oes., Vol. I (1883) , pp. 150-55 ; also Sitzungsber. d. kais, Akad. d. Wiss. zu Wien, math.- 

 nat. hist. Klasse, Vol. I (1887), p. 221. 



2 J. M. Janse, " Plasmolytische Versuche an Algen," Bot. Centralbl,, Vol. XXXII 

 (1887), pp. 21-6; idem, "Die Permeabilitat des Protoplasma," Verslag. en Mededeel. 

 d. k. Akad. v. Wetensch. te Amsterdam, 3 Eeihe, Vol. IV (1888), p. 332. 



3 A. WiELEE, " Plasmolytische Versuche mit unverletzten Phanerogamen," Ber. 

 d. deutsch. bot. Ges., Vol. V (1887), pp. 375-80. 



