

532 



ME. S. LE M. MOORE S STUDIES 



time ; while for the slaty colour with oamic acid one must wait 

 half an hour or so. Potassium bichromate also is slow in its 

 action. 



The close relation between the colouring-matters which occur 

 dissolved in the cell-sap, and are known under the general term 

 anthocyan, is admitted by most physiologists *. This is what 



o 



Escallonia 



scales) 



The red colour 



























is almost instantly turned a fine deep green, which soon passes 

 into yellow and this into brown. If caustic potash alone is used, 

 the effect is the same except that the brown stage is not reached. 

 Here, too, one sees how valuable an aid Nessler's fluid is likely 

 to prove : for instance, De Vries f, in his study of the contents 

 of Drosera tentacle-cells, used Moll's test for the discovery of 

 tannin, and this involved waiting for twenty-four hours, whereas 

 with the new reagent his inquiry would have been answered in a 

 few minutes. 



Failure might, perhaps, be deemed probable with cells con- 

 taining much free acid, since the action of Nessler's fluid is due 

 in large measure to an alkali. But, so far as concerns two of the 

 commonest acids occurring in plants, this is not the case, for on 

 charging a solution of tannic acid with either citric or oxalic 

 acid, the precipitate is still obtained with Nessler's fluid. 



Added to a solution of tannin or tannic acid Nessler's fluid 

 throws down a precipitate which is momentarily of a reddish colour, 

 then changing to brown. Other reactions are as follows : 





■ 



. 



With Gallic Acid 

 „ Pyrogallol 



„ Pyrocatechin 



it 



gives a grey 



?> 



>> 



„ Protocatechic Acid 



» 



a brown precipitate immediately 



(no momentary red). 



a deep green precipitate, soon 

 turning to greenish brown. 



a dirty-green precipitate. 



These precipitates are probably all of them oxidation-products; 









On this point see, for instance, Wigand, Bot. Zeit. 1862, and Forsch. aus 

 d.bot. Garten zu Marburg, Heft ii. (1887) ; Wiesner, Bot. Zeit. 186^ Went. 

 Jahrb. f. wiss. Bot. Band 19; Pick, Bot. Centralbl. 1883; Dennert, Bot. Cen- 





1 





tralbl. 1889. 







1 



■ 





QQa 





















■ 





* 







■ 



, 



H ■ * f ~ * . *. 







• 



'J 



