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the same fungus growing on different media and in different con- 
ditions ? : 
This last question is vital, and I propose to examine it a little more 
closely. You are aware of the excitement which arose when the poly- 
morphism of the Fungi, as it was termed, was first brought forward by 
the Tulasnes and followed up with such critical acumen by De Bary 
and his school. We now look on the then marvellous cases of 
Sclerotinia, Eurotium, Puccinia and many other instances with equa- 
nimity, and smile at the wild dismay of the mycologists of those days 
who could not see the trend of events, and that much of this poly- 
morphism was of the same order as we should institute by having 
different names for corn in the blade and corn in the ear.. Much 
more subtle are the cases with which Eriksson has now familiarised 
us—the varietal forms or races of Puccinia graminis—or which Hansen 
has shown to exist in the cultivated yeasts. These must be put at the 
other extreme as cases of, not polymorphism—because we cannot per- 
ceive the differences in form—but polyergism, if I may coin the term 
to express their salient features of differences in physiological activity. 
Between these two extremes we are beginning to recognise that 
there exists a kind of polymorphism in which direct effects of nutrition 
are observable, and not mere differences of developmental stages. 
Plenty of instances can be given of the direct effects of nutrition. 
Brefeld showed that if you go on growing an Ustilago in certain 
nutritive media it yields nothing but yeast-forms for months and 
years, and no one would suspect these to have anything in common. 
with the Ustilago developed on a cereal. 
Planchon’s recent investigations on the effect of food-materials on 
Dematium and other Fungi lead to the same conclusions. I have 
myself shown quite conclusively that Dematium pullulans may de- 
velope in the form known as Coniothecium on pine sawdust, as a 
Torula on certain other solid media, as a Yeast in certain liquids, 
while the typical Dematium condition is regularly maintained on 
saccharine gelatine media, all at ordinary temperatures and growing 
side by side. 
Equally conclusive are the remarkable results recently published 
by Klebs, showing that the reproduction of Fungi, and the kind of 
spore produced, depend in the first instance on definite conditions 
of nutrition. Klebs showed that it is possible to take a fungus, such 
as Saprolegnia, and cultivate it for months, and even years, on a suit- 
able food-medium, where it grows admirably, but never produces 
either zoosporangia or oogonia. Klebs found that if he sowed this 
fungus on the following medium, 
Gelatine Sik . or 2k) 2, SELUAS 
Extract of Mea we .. 2 grams 
Pap water < 4. si .se4 63 CULM, 
it grows admirably, and in two or three days formed an abundant 
mycelium. The same result was obtained if a bit of this sterile my- 
celium was transplanted by means of a needle into a solution made 
by boiling 5 peas in 50 c.cm. of tap water, 

