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 Pénicillium, 
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.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 i 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 i cc. of a i 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. 
