IN VEGETABLE BIOLOGY. 251 



(1) Stored at or near the surface it is withdrawn from the 



drama of metabolism going forward in other parts, inter- 

 ference with which drama might be expected were it 

 present in too great quantity. 



(2) It performs the police function of warding off enemies on 



account of its bitterness. 



(3) 



with alkalis travel to the surface to be excreted from the 

 plant by the agency of the ammonia of dew, rain-water, 

 and the soil. 



"We will take first the leaf of the Primrose, and, by simply 

 tearing off pieces of its epiderm, study the reactions of the 

 tannin stored up in the idioblasts of that tissue. 



Proteid Reactions of Tannin of Primrose Epiderm. — A fairly 

 good (M) reaction : the colour is a brown-pink, so deep in many 



of the idioblasts as to appear quite black : the pink colour I 

 could not get in many of the trichomal cells — the colour here 

 was usually brown, ultimately becoming yellow. A very good 

 (X) reaction. "With regard to (E), in a syrupy solution hydric 

 sulphate throws down a grey precipitate in the idioblasts ; this 

 soon becomes a beautiful warm brown, and finally almost pink. 



Failure of other Proteid Reactions with Primrose Tannin. — 

 (C) fails ; copper sulphate gives a grey-brown colour, which turns 

 to orange when caustic potash is run in. 



Gnezda's test (nickel sulphate and ammonia) also fails : 

 instead of a blue or a yellow, becoming yellow or orange re- 

 spectively on addition of caustic potash, Primrose tannin takes a 

 pinkish-grey, not appreciably changing with caustic potash. 



Proteid Reaction of the Tannin of the Ivy.—(M) reaction not 

 very good : indeed it is seen properly only when tannin is aggre- 

 gated at the base or the apex of a trichomal cell — here, however, 

 it is a fair reaction. Possibly the cuticularization of the walls of 

 the hairs causes interference with the result, since tannin in the 

 fundamental tissue of the stem and petiole reacts well. 



(X) succeeds admirably, but the precaution must be taken of 

 only warming the nitric acid, otherwise all the tannin will diffuse 

 out of the cells. 



(R) frequently succeeds perfectly, but the effect must be 

 carefully watched for, as it soon passes off. 



Copper sulphate gives a pale grey or greenish grey, becoming 

 "gut brown or greenish brown on boiling. 



u2 



