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on the other side of which an attractive food-material such as a sugar 
has been placed, so that our saprophyte here not only turns towards 
the membrane, but excretes a solvent enzyme and dissolves its way 
through it, and so gets at the sugar just as a parasite would do. On 
the other hand many parasites can be easily cultivated for years in 
artificial media—e.g., Ustilaginee. Yet even these very mould-fungi 
so remarkable for their omnivorous heterotrophy exert, so to speak, 
a distinct choice when two or more carbon compounds are. offered 
them together, as shown by the fact that Penecillium is employed by 
the chemists to split racemic compounds. In other words, if Penz- 
cillium or Aspergillus is offered tartaric acid as a source of carbon, 
it splits this into its optically positive and negative varieties, and so 
long as there is optically positive acid present the fungus leaves the 
other variety severely alone. —S 
Again, although Aspergillus can feed on glycerine, it will pick out 
the smallest traces of dextrose from a mixture with glycerine before 
attacking the latter, whereas it prefers acetic acid to dextrose in a 
mixture of these two although acetic acid itself is, like glycerine, a 
poor food. . 
Again, Eurotiopsis Gayoni, a most remarkable fungus found on 
boiled starch, can obtain its carbon from Dextrose, Levulose, Maltose, 
Lactose and numerous other such substances, and yet is totally in- 
capable of utilising cane-sugar or Inulin, notwithstanding the close 
relationships of these carbo-hydrates to sugars and starches. 
Many other instances can be given where a fungus selects one sub- 
stance in preference to another, although the latter may be the better 
food-material as judged by the general behaviour of organisms to- 
wards it. 
Such considerations, and numerous experiments based on them, 
lead to the conclusion that we cannot classify or arrange the food- 
materials of Fungi according to any chemical or physical scheme. 
Nageli’s conclusions that compounds containing C. and O. directly 
connected could not be assimilated, and that C. H. groups are useless 
unless two or more atoms of carbon are linked together, were alike 
premature and inaccurate, as shown by the feeding of certain Fungi 
on formic acid or methyl alcohol, each containing but one C. atom. 
Equally is it impossible to estimate the nutritive value of a food- 
material according to its calorific value, otherwise fat ought to be 
always a better food than glue, and cane-sugar better than either, 
whereas, as I have recently shown, Onygena equina refuses both fat 
and sugar, and demands the glue, and Phycomyces nitens revels in fatty 
oils, as was well exemplified by the enormous growths of that fungus 
I saw at a burnt oil mill last winter. The fact stands out plainly that 
we do not know what decides the nutrient value—z.e., the smallest 
quantity of carbonaceous substance consumed by unit-weight of plant 
in unit of time—of any carbo-hydrate or other organic substance, and 
must conclude that the protoplasmic activities are so attuned to par- 
ticular food-supplies that they refuse to readily change their habits—- 
I say readily, because we know of many cases where a fungus can be 
