618 Microscopical Fungi Infesting our Cereals. [October, | 
Thus we see the Æcidium producing Uredo, the Uredo Puc- 
cinia, and the Puccinia again Æcidium, and we have the inter- 
esting fact, that fungi of an apparently unlike structure, which 
have been hitherto described as belonging to different genera, and 
which are actually to be found on entirely different plants, are in 
reality but sucessive forms of development of the same parasite. 
By this discovery of De Bary, the attention of a number -of 
mycologists was directed to other species of rusts. Numerous 
experiments have been made, and thus the connection of a num- 
ber of hitherto separated forms has been found out. We know, 
for instance, that one species of Uredo, U. straminis, which 
destroys the glumes and attacks the ovaries of wheat-ears, and 
which in 1862, in Denmark, caused a damage of nearly a million 
of dollars, has its Æcidium form on the several Boraginee ; that 
a disease on pear trees, destructive to the young leaves and 
ovaries, and known as Restelia cancellata, is the Atcidium form 
of a Uredo growing in early spring on Juniperus and hitherto 
described as Gymunosporangium. 
In some rusts the winter spores present a form at the same 
time very elegant and quite different from Fuccinia. So we see 
towards autumn the under surface of blackberry and rose leaves 
spotted all over with little blackish powdery tufts of the so-called 
blackberry brand or Phragmidium. These tufts are composed of 
four or five-celled elegantly granulated spores, produced on long 
hyaline peduncles. In the same places where we find them now 
we would have met a month ago the one-celled Uredo spores, 
and it is quite interesting to observe under a lens from day tO 
day how (beginning at the circumference and moving towards the 
center) the dark winter spores are gradually superseding those of 
Uredo. This connection has also been discovered but recently. 
In the same way the dimorphism of several other rusts and 
brands has been defined. However, we are as yet.ignorant as to 
the development of a good many other species, and there is con- 
sequently a vast and at the same time highly interesting field left 
for further investigation. | 
IV. Mildew.—* Mildew,” says M. C. Cooke in his Parasitic 
Fungi, “is one of those loose terms which represent no definite 
idea, or a different one to different individuals.” It may be so In 
_ England; American farmers, however, as well as horticulturists of 
_ my acquaintance, unanimously apply the term to the several spectes- 
