igii] Francis Ernest Lloyd 23 



it may take. Its flow is quite limited and jerky ; its limit of capac- 

 ity for imbibition is evidently quickly reached. 



The tannin-mass stains blue with iron salts, but remains homo- 

 geneous, while the free tannin appears as a precipitate, especially 

 in situations nearer the cell. With ammoniacal potassium ferri- 

 cyanid Solution/* a rose-red color reaction is evidence of free 

 tannin, while the tannin-mass gives a brownish reaction. Alkaloids 

 produce in the tannin-mass, at first especially on its surface, a 

 pronounced granulation. At the same time, they appear to have 

 a coagulating effect upon the postulated second colloid, so that the 

 superficial layers are hardened. This results in the repeated erup- 

 tion of the softer, uncoagulated inner portions through the frac- 

 tures of the outer. Upon the exposure of a new surface, fresh 

 precipitation is at once seen. The rapidity and extent of coagula- 

 tion depends upon the strength of the reagent. A i per cent. Solu- 

 tion of caffein is too strong for careful and deliberate Observation. 

 In practice I have repeated observations with either gradually 

 increased or diminished strengths, between i per cent. and o.i per 

 cent. and even less. The penetration of these reagents into the 

 cell permits the conclusion that, upon reaching the tannin-mass or 

 a portion of it remaining undisturbed, the course of the reaction 

 is the same as in the erupted portion. One finds no evidence that 

 there is any free tannin beyond the surface of the tannin-mass, nor 

 in the sap-vacuoles. The alkaloids are of Superlative value in 

 showing the latter to be true. I have been able to follow the course 

 of the reagent through the protoplasm into a vacuole and into the 

 contiguous tannin-mass, without observing a trace of precipitate 

 in the vacuole (fig. 8). Proof that it has penetrated the vacuole 

 is seen in the rate of penetration and in the circumstance that the 

 protoplasm becomes clear and translucent. An additional proof 

 that the free tannin remains within the confines of the tannin-mass 



"Allen, A. H., Chemistry applied to the detection of adulteration. Chem- 

 ical News, 29: 169, 189. 17 Apr. 1874. I beheve that this is the first time 

 that this reagent has been used in microchemical work. It is very excellent 

 for the demonstration of certain difficult points, because of the delicacy of 

 the reaction (it detects one part of tannin in 10,000 parts of water according 

 to Allen and Fletcher), because of the distinct, but transparent reactions of 

 the tannin-mass, and because of the rapidity of action. 



