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POPULAR SCIENCE REVIEW. 
ment (Plate VII. fig. 22). These bilocular, or two-celled spores 
are those of the “ corn mildew ” {Puccinia graminis) } which 
may be produced in the same pustules, and from the same 
mycelium, as the “ corn rust,” but which some mycologists 
consider to be a distinct fungus, others only a modification or 
stage of the same fungus. After an examination of the dif- 
ferent forms in the allied genera to which this paper is devoted, 
we shall be able with less of explanation and circumlocution 
to canvass these two conflicting opinions. 
Let us proceed, for the third and last time, to our cornfield, 
when the corn is nearly or fully ripe, or let us look over any 
bundle of straw, and we shall find blackish spots from the size 
of a pin's head to an inch in length, mostly on the sheaths of 
the leaves, often on the culm itself. This is the fully deve- 
loped mildew , and when once seen is not likely afterwards 
to be confounded with any other parasite on straw (fig. 20). 
The drawings of Bauer have already been alluded to. Bauer 
was botanical draughtsman to George III., and his exquisite 
drawings, both of the germination of wheat and the fungi 
which infest it, are marvels of artistic skill. A reduced figure 
from part of one of his drawings is given in the plate (fig. 21) 
exhibiting a tuft of the bilocular spores of Puccinia graminis 
bursting through a piece of wheat straw. These closely- 
packed tufts or masses of spores, when examined with a com- 
mon lens, seem, at first, to resemble the minute sorus of some 
species of fern ; but when seen with higher powers, the appa- 
rent resemblance gives place to something very different. 
The tufts consist of multitudes of stalked bodies, termed 
spores, which are constricted in the middle and narrowed 
towards either extremity. The partition, or septum, thrown 
across the spore at the constriction, separates it into two 
portions, each of which consists of a cell- wall enclosing an 
inner vesicle filled with the endochrome (fig. 22) or granular 
contents, in which a nucleus may often be made out. This 
species of Puccinia is very common on all the cereals culti- 
vated in this country, and on many of the grasses. A variety 
found on the reed was at one time considered a distinct species, 
but the difference does not seem sufficient to warrant a sepa- 
ration. However near some other of the recognized species 
may seem to approximate in the form of the spores, a very 
embryo botanist will not fail to observe the distinctive features 
in the spores of the corn mildew, and speedily recognize them 
amongst a host of others ; subject as they may be to slight 
deviations in form, resulting either from external pressure, 
checks in development, or other accidental circumstances, or 
the variations of age. 
There is no doubt in the minds of agriculturists, botanists. 
