AS RESERVE-MATERIAL IN PLANTS. 



27 



To select objects free of glucose, is not difficult, but rarer 

 are such as unite with an abundance of proteids the absence of 

 tannin, seemingly a frequent by-product in the synthesis of 

 proteids. It collects in the proteosomes in combination with 

 albumen. — We have shown however, that tannin might be used 

 as a source of carbon in the formation of proteids under favorable 

 circumstances. These experiments were made with Penicillium, 

 cultivated in nutrifying solutions containing as sole organic sub- 

 stance tannin. The produced mass of the fungus amounted to 

 12,4 per cent of the tannin applied, after a growth of four weeks, 

 at the end of which time no trace of tannin was present any 

 longer. r) This result led us to experiments with Spirogyra 2) and 

 indeed the tannin disappeared, the best reactions failed finally, 

 and when the cells were boiled with a little water, neither the 

 acqueous liquid nor the cells themselves showed any reaction 

 with a 1 per cent solution of nitrate of silver supersaturated 

 with ammonia ; hence it was evident that neither a soluble 

 nor an insoluble reducing substance was present any longer 

 in the killed cells. Still, the proteosomes were capable, even 

 after treatment with ammonia (1 p. m.), of reducing even very 

 highly diluted alkaline silver solutions, the globules thereby turning 

 black. Such proteosomes however as were changed by acetic 

 acid, or by any other death of the cells were found incapable 

 of reducing the same silversolutions, even after 24 hours contact. 

 This silver reagent was always left with the objects in the dark, 

 and was applied in a highly diluted state, because it is charac- 

 teristic of aldehydegroups, to bring on a silver reduction in far 

 greater dilutions, than many other reducing substances or atomic 

 groups. A suitable silver solution may be obtained by super- 

 saturating 1 cc. of a 1 per cent solution of silver-nitrate with 

 ammonia, adding a few drops of a diluted solution of caustic 

 potassa and diluting this mixture to one liter with distilled 

 water. This solution contains 100000 parts of water for 1 part 

 of silver-nitrate employed (present now as oxyde in solution) and 

 is still easily affected by aldehydes. 



1) Botan. Centralbl. 1889 Nr. 39. 



2) The smaller kinds of Spirogyra are sometimes found also in nature free 

 of tannin. Of the larger kinds most tannin is found in Sp. crassa and Sp. majuscula, 

 which therefore are not so favorable for these experiments, as other kinds. 



