274 Harshberger : Water-storing tubers 



strong cupric sulphate is used. Absolute alcohol does not cause 

 the deposit of inulin crystals, and the absence of inorganic crystals 

 is very noticeable. Imbedded in the protoplasm of the cells and 

 scattered through it are granules which suggest starch, although 

 the iodine test fails to show its presence in the fresh tubers. To 

 be absolutely sure that these granules were not starch grains, I 

 applied dilute sulphuric acid, washed off the acid with distilled water, 

 and treated the sections with iodine. No reaction took place which 

 would indicate the presence of starch. The presence of tannin, 

 especially in the partially mature tubers, was revealed by the action 

 of the j uice on a bright razor blade. The bluish-black discoloration 

 produced showed the formation of tannate of iron. This test is 

 corroborated by a microchemic reaction in which the starch-like 

 granules take part! Tannin vesicles have been observed in various 

 phanerogams. These tannin vesicles always arise, as Klercker has 

 shown, in the protoplasm, from which they are most probably sep- 

 arated by a true precipitation membrane of albumen tannate. 

 Whether they contain other substances than tannins cannot at 

 present be certainly stated. Especially useful in determining the 

 presence of tannin is Pfeffer's staining intra vitam with methylene- 



m 



blue. In a solution of this pigment, the cell sap which contains 

 tannin and the tannin vesicles take up the blue color. This reagent 

 applied to thick sections of Nephrolepis tubers produced a blue 

 color in the starch-like granules (figure 7) which had not reacted 

 with the application of iodine, Bismarck brown, water-eosin, sul- 



phuric acid and iodine, and acetic acid. That this test is decisive 

 with reference to these granules is proved, I believe, by the pres- 

 ence of sugar in the older tubers, such sugar having been derived 

 from the stored tannin. It is a known chemical fact that tannin 

 may be converted into sugar by a complex reaction, and in all 

 probability, although I have been unable to prove it, the tannin 

 present in the living parenchyma-cells of the above fern species 

 slowly transformed into sugar which reacts in the ;older tubers to 

 Fehling's solution. 



The character of the reserve material stored in the tubers having 

 been determined, it can be stated definitely that water storage is the 

 principal function of them. The amount of water stored is very 

 considerable. If a tuber is left in the sun to dry, it loses practi- 



is 



