80 
NOMAD FUNGI. 
liypha from which they originated, which breaks off with them as 
a kind of stalk ; each spore consists of two cells, separated by a 
transverse partition, or rather two spores are produced on each hypha, 
for each cell of the compound spore is capable of independent germina¬ 
tion. The .Greatest difference of all is, however, in the cuticle of the 
spore, which in these is greatly thickened and strengthened, in the 
same way as the outer surface of the epidermal cells of many leaves 
is cuticularised, in order to enable it the better to resist the attacks 
of the weather. This last form of fungus is called a Puccinia, and 
our species is known as Pncciiiid viohiruiii. 
Now undoubtedly the first impulse of the student, on seeing these 
various kinds of fungi, would be to class them as three distinct species, 
belonging to three distinct genera, and placed respectively in the three 
orders which have been mentioned above. But this impulse, though 
natural, could not stand the test of a more careful examination. Our 
student would find the same sequence of phenomena on other species 
of plants. The common Epilobiums would provide him with three 
fungi, successively making their appearance on the leaves, in the same 
way and in the same order, viz., CEcidium epilohii, Tricliohasis epilohii, 
and Pucxinia pulvendenta. The species of Allium, of Primula, of 
Mentha, of Gralium, of Sanicula, and many others, all tell the same tale. 
This should have awakened suspicion, hut at first apparently did not. 
Moreover, the Uredo and Puccinia-forms appear, as I have said, often on 
the same leaves at the same time, and are obviously seen to spring from 
the same mycelium, not only in the species which I have mentioned, 
but in very many others. This fact, when fully brought to light, was 
so far conclusive ; and the phenomenon was known under the name of 
Dimorphism. Those who have read Mr. Cooke’s useful little book on 
Microscopic Fungi will remember that he devotes a chapter to the 
exposition of this theory of Dimorphism, and in his Handbook the 
theory is practically followed up by the arrangement of the various 
forms of Uredo with the species of Puccinia to which they belong, so 
far as that was known. It is true that Cooke calls most of these 
Uredos Trichohasis, and professes to distinguish between the two 
genera by assigning to the spores of the latter the possession of a foot¬ 
stalk, while the spores of Uredo, he says, “ have no foot-stalk at any 
stage of their existence.” In fact, in the generic character of Uredo 
he seems to assert that the spores of Uredo are developed by a kind 
of segregation of the contents of certain hyphal cells, that is, by free 
cell-formation. But this is totally untrue. The spores of Uredo are 
formed by constriction from the end of a hyphal filament, which, 
when thus engaged, is called a basidium. There is no difference 
between Uredo and Trichobasis, except that in the latter case, in a 
few instances, a small fragment of the basidium remains attached t# 
the spore. 
But while the Dimorphism of these fungi was admitted, the fact 
which still remained behind, namely their Trimorphism, was as yet 
undiscovered. If the case had been with all the Uredineae as with 
