264 
IOWA ACADEMY OF SCIENCE Voi.. XXVIII, 1921 
species. Of course this cursory examination should be followed 
by placing some of the material under the compound microscope. 
The student can then make a further study, if he has fresh ma- 
terial, of the germination of the conidia and if the proper material 
is at hand inoculation experiments can be made in the greenhouse 
producing the disease on the wild uncultivated grape. It goes 
without saying that every well regulated laboratory in plant path- 
ology should have a greenhouse, though this is not absolutely 
. necessary. Seedlings of radish and mustard can be grown in 
pots, covered with bell jars to get the proper moisture relations 
and then one can produce the downy mildew of mustards on these 
plants, or the white rust. Eet us take another well known illus- 
tration — the common wheat rust. What student has not seen 
the yellow spot on the barberry leaf with the little black specks, 
the spermogonia, and on the lower surface the cuplike bodies? 
With a good hand lens the fringed cup and spores may be seen. 
One who knows can tell the uredo sori of Puccinia coronata from 
P. graminis. How easy it is also to recognize by macroscopic 
characters the difference between Gymnosporangiiim macropus 
and G. glohosum, a difference between the perennial and annual 
gall of the two species. 
No one could make a mistake in the identification of the com- 
mon bunt of wheat (Tilltia foetens) and loose smut of wheat 
(Ustilago Tritici). One could hardly make a mistake between 
loose smut of oats {Ustilago avenae) and the covered loose smut 
{Ustilago laevis). In a study of the macroscopic characters of 
such diseases as Illinois canker one could hardly make a mistake. 
Nor could we make a mistake in the two forms of plum pockets 
commonly found on the wild plum, the Hxoascus prunii and B. 
communis, the former on the plum and the latter on branches of 
the Miner plum. There is nothing .else exactly like the black knot 
of the plum and one should be able to place it without much 
trouble. 
In modern courses in plant pathology growing pure cultures form 
a part of the regular work. Pure cultures of the organism can be 
used to inoculate plants and the lesions produced may be studied. 
Of course inoculations with diseased plant material can be made 
with such diseases as sorghum blight, apple blight and rust. 
I hope you will pardon this somewhat disconnected discussion 
of the topic before us. 
Department oE Botany 
Iowa State College 
