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130 
monium acetate, with the result that growth occurs but is worse and 
worse as we go down the list. A still more accurate series of results 
is got by using ammonium nitrate as the source of nitrogen through- 
out—of course with the minerals also—and varying the source of 
carbon. The growth will then be found to be worse and worse as we 
go down the following list. Grape-sugar, cane-sugar, peptone, albu- 
men, quinic acid, tartaric acid, citric acid, asparagin, acetic acid, 
butyric acid, ethyl alcohol, benzoic acid, propylamine, methylamine, 
phenol, formic acid. , 
That any fungus should be able to grow at all in some of these 
media is remarkable enough, and it should be noted that most of the 
lower numbers on the list are utterly useless to most Fungi. 
Further research has shown that these common moulds can secrete 
various kinds of acids and enzymes, and their universal ‘distribution 
and adaptation to all kinds of food-materials (heterotrophy) evidently 
depend on these powers. Their occurrence in the chemicals of 
druggists’ shops, even in solutions of arsenious acid, picric acid, 
copper-sulphate and other poisons, the power of penetrating wood 
which I have shown Penicillium to possess, and the existence in them 
of proteolytic, diastatic, inverting, and other enzymes which attack 
proteids, cellulose, sugars, fats, etc.,all go to explain their ubiquity. 
What a different case seems to be presented when we turn to a 
parasiticfungus such as a Uredine, or other form which can only live 
on some special host-plant and cannot be cultivated in artificial media. 
And yet the difference is more in degree than in kind, for recent 
researches have convinced us that the parasite contains and requires 
the same elements and compounds as the saprophyte, only it has had 
to adapt itself to certain peculiar difficulties in obtaining it. 
I might perhaps compare the roving saprophyte to a vagabond in 
a land of plenty where, his tastes not being fastidious, he finds abun- 
dance of suitable food lying around, as our cousins say, on all hands, 
to be picked up without restraint ; whereas the parasite has been so 
long used to having his food highly prepared and specially served 
that, although he has to enter stomata, pierce cell-walls and cause all 
sorts of locks, bolts and bars to fall asunder before he can get at the 
stored and manufactured tit-bits in the cells attacked, we must regard 
him as a sort of aristocrat—a burglarious aristocrat, if you like, but a 
highly bred and fastidious individual nevertheless. 
It seems at first as if immeasurable differences separated these 
parasites from the ubiquitous moulds, but closer investigation raises 
suspicions as to the validity of such a conclusion. On the one hand 
‘t has been shown that if we inject a little sugar into a living leaf, so 
that an excess of this dainty is presented, even so irreclaimable 4 
saprophytic vagabond as Penicillium will creep through the stomata. 
and penetrate the leaf-passages, behaving to all intents and purposes 
like a parasite ; moreover, it will enter the medullary rays and other 
tissues of wood under certain circumstances quite like a timber-para- 
site. Nay, it is possible to induce Penicillium and Aspergillus to 
penetrate epidermal cell-walls or even artificial cellulose membranes 

