356 
The teleutospores are sometimes found in a semi-rudimentary condi¬ 
tion. The spots are found on both surfaces of the leaf. The effects on 
the nectarine are similar to those on the peach. 
In southern California the apricot is not commonly affected by rust 
to as great an extent as are the prune and peach, although usually the 
disease may be seen in nearly all orchards in the coast region. Some¬ 
times the margin of the leaf is most affected, but all portions may be 
diseased. As in the previously mentioned cases, the uredospores pre¬ 
dominate. The teleutospores are less abundant than upon the peach. 
The two forms when present are large and well developed. The rust 
produces on the apricot small, irregular, reddish, scar-like spots, which 
show on both surfaces of the leaf. The under surface finally turns a 
yellowish color and becomes powdery with the abundant uredospores. 
When badly diseased, the whole leaf may turn yellow and fall prema¬ 
turely. As yet, however, I have not seen this tree entirely defoliated 
by the disease. 
In the East the cherry is more or less injured by the same parasite, 
and I have no doubt that this is also the case for portions of the Pacific 
coast. As the cherry is neither extensively nor successfully grown in 
the warmer valleys of southern California, we have not had sufficient 
material for a general study. Farther north, and in the more elevated 
regions of the southern portion, where this fruit thrives, the parasite 
may be looked for. 
The almond is infected by the rust to a limited degree. Both teleuto¬ 
spores and uredospores have been found, although the former were 
rare in the material examined. The teleutospores were rather small. 
The uredospores varied greatly in size and form, and in thickness of 
their walls. Some were dark and nearly spherical, while others were 
normal in form and thickness. So far as seen, the almond is not defoli¬ 
ated in California by the parasite. 
TREATMENT. 
The prune rust fungus is a truly endophytic parasite, vegetating and 
obtaining its nourishment wholly within the tissues of its host, and 
only appearing at the surface of the leaf for spore formation. This 
makes it evident that the treatment for the disease should be preventive 
in its nature. The application of sprays or other treatment after the 
parasite is within the tissues of its host can not act remedially and can 
only serve to prevent further infection. 
The serious action of this parasite during the summer of 1891, and the 
fact that its attacks were more general and severe than in 18S9, seemed 
to indicate that the disease was increasing, and it was decided to under¬ 
take a series of preventive experiments. This was the more necessary 
because the climatic conditions are very different in the coast valleys 
of southern California from those of the portions of the Eastern States 
