Il8 BOTANICAL MICROTECHNIQUE. 



out the carbonate. But after a time they lose this capacity 

 and are gradually transformed into solid and brittle bodies. 

 The same precipitates are formed when tannin and ammo- 

 nium carbonate are brought together in a test-tube ; but if 

 the carbonate solution be very dilute, it only occurs when a 

 gradual accumulation of this salt is made possible ; which 

 Klercker (I, 42) accomplished by placing the tannin solution 

 in a capillary tube sealed at one end, and then putting the 

 whole in a large vessel filled with the carbonate solution. 

 Since, according to Klercker's researches, these precipitates 

 have been seen only in cells containing tannin and always 

 give the tannin reactions with potassium bichromate and 

 other reagents, it would appear that the alkaline carbonates 

 may well be used as reagents for tannin. 



But not all tannins are precipitated by them ; for instance, 

 gallic acid is not. 



207. In order to carry out the reaction described, sections 

 of the plants to be studied are placed on the slide in a drop 

 of a 1-5$ solution of an alkaline carbonate or the plants 

 are cultivated for some time in a very dilute, about .02$, 

 -solution. The carbonates of potassium, sodium, and ammo- 

 nium seem to be equally active, but the ammonium salt has 

 been most used. Ammonium chloride seems also to act in 

 the same way; but the bicarbonates produce no precipitate. 

 A very suitable object for study is found in the stem or 



petiole of Ricinus communis, 

 which contain red pigment-cells 

 in the pith and bark. If longi- 

 tudinal sections of these are 

 jj placed in a \% ammonium car- 



>. -Ceils from the pithof the peti- bonate solution, granular pre- 

 f cipitates appear in a short time, 

 which gradually collect together 



and, after about an hour, have drawn almost the entire pig- 

 ment to themselves (cf. Fig. 30). Spirogyra cells which 

 contain tannin also form excellent objects for study, since a 

 precipitate is almost immediately formed in them by ammo- 

 nium carbonate. 



