1922] KNUDSON—ORCHID SEEDS ar 
as well as other soluble organic and inorganic substances. The 
significant fact is that at the outset some soluble organic substances 
are present. 
In addition to the soluble substances present, which apparently 
are not sufficient in quantity nor suitable as regards quality to 
permit of germination, there are to be considered the insoluble 
organic substances, pentosans, starch, and organic nitrogenous 
substances.. Digestion of starch by the fungus would augment 
the concentration of sugar, and digestion of the organic nitrogenous 
substances might produce certain products which would make 
possible the germination of the seeds. 
In my experiments it is true that the sugar used generally was 
of a relatively high concentration, but in the case of Epidendron, 
germination was obtained on 0.2 per cent glucose, which sugar is 
not particularly favorable for growth. That other substances 
besides sugar exert a pronounced influence is shown by the experi- 
ments on the beneficial effects of adding certain plant extracts to 
the glucose-containing solutions. The fact that other substances 
besides sugars may be important in the germination is shown by 
the experiments in which germination was obtained on decoctions 
of yeast, wheat grains, or of potato. All of these extracts contained - 
less than 0.02 per cent total sugar. The experiments on the 
influence of Bacillus radicicola also lend weight to the idea that 
certain extraneous products may markedly influence germination. 
BurRGErFrF, in certain of his experiments, used 2 per cent salep, 
but in other experiments he used starch, sucrose, or glucose. The 
explanations offered with respect to the function of the fungus in 
discussing BERNARD’s work may be used to account for the results 
obtained by Burcrerr. There may appear to be rather more 
difficulty in explaining the function of the fungus in the cultures 
containing either glucose or sucrose. It will be necessary to discuss 
these in more detail. 
In one experiment, seeds of Cattleya were sown in a tube con- 
taining a nutrient solution plus 0.33 per cent sucrose. After three 
months the embryos were 0.4-0.5 mm. in width. Then, according 
to BurceErr, they remained stationary. Cultures four months old, 
inoculated and maintained in the dark at 23° C., produced the first 
