Reed—Infection Experiments. 
145 
trols. Under these conditions the leaves retained their vitality 
long enough to determine whether infection would take place. 
The inoculations were made by removing with a scalpel a few 
spores from an infected leaf and applying them to the leaf to be 
inoculated. As the spores, under ordinary conditions, are light 
and dry, it was difficult to get them to stick to the leaf to be in¬ 
oculated. This difficulty was overcome by placing infected 
leaves on a moist filter paper in a Petri dish and leaving them a 
few hours. In this way a very abundant supply of moist con¬ 
i'dia was secured which readily adhered to a leaf when applied. 
Care had to be taken not to leave the spores too long before 
using them as they readily germinate under such conditions. 
The time elapsing between inoculation and the first appearance 
of infection was fairly 'constant. Patches of mycelium ap¬ 
peared in from three to four days if infection occurred at all. 
By the fifth day conidia were very abundant. The first obser¬ 
vation recorded was made when the conidia had become abund¬ 
ant, not at the first appearance of the mycelium. 
Before taking up the detailed account of my experiments it 
will be interesting to note some general differences in the be¬ 
haviour of the mildew on the rye and blue grass. On the young 
rj T e seedlings the mildew spread very rapidly. When the 
leaves of seedlings placed beside well infected plants showed 
signs of infection, it was only two or three days until all of the 
seedlings were nearly covered with patches of mycelium bearing 
abundant conidia. In the case of Poa pratensis the conidia 
were not produced nearly so abundantly, nor did the fungus 
spread so rapidly. In one case a tuft of P. pratensis which was 
growing about two feet from another that was infected re¬ 
mained free from the mildew for almost three weeks. Then at 
first only a very few patches of mycelium appeared. It was 
fully two weeks longer before the mildew had spread over the 
entire tuft of the grass although the sod only covered an area 
about three inches in diameter. 
The mycelium and conidia also differed markedly in color on 
the two host plants. The growths on the blue grass were pure 
"white while those on the rye were quite pinkish in color. 
When infected leaves were left in a Petri dish they gradually 
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