30 BULLETIN 957, U. S. DEPARTMENT OF AGRICULTURE. 
Rhoads 10 came to the conclusion that the disease spreads from the 
original point of infection upward and downward at about equal 
rates of progress. Posey and Gravatt, and Rhoads found that it 
spreads at nearly the same rate laterally on both sides. Progress 
upward and downward is usually more rapid than it is sidewise. It 
also appeared that in infections not yet bearing eecia, the point of 
greatest swelling is where infection first took place and where ascia 
will be first produced. Very often a dead twig or a leaf scar shows 
very plainly the original point of entrance of the fungus to the bark. 
Rhoads concluded that infections on shaded lower branches do not 
spread as rapidly as those on vigorously growing ones, but Posey and 
Gravatt u find that the former are more likely to be attacked by 
secondary fungi, which soon kill the branches. 
Posey and Gravatt 11 found that there are more or less frequent 
instances in old infected areas of white pines where the infections on 
lateral branches die out. The statement (131, p. 16; 141, p. 5) that 
trees once infected with this fungus never recover was largely based 
upon studies of trunk infections. Like all rules, it has its exceptions, 
as here indicated. At Kittery Point, Me., Posey and Gravatt 
studied one of the -oldest outbreaks in North America. Trees of all 
ages from a few years up to 50 or 75 were infected. Here it was found 
that secondary fungi often kill the blister rust in an infected branch 
and that increasing suppression of lower branches killed many of the 
infected ones before the blister rust spread to the trunk of the tree. 
It was found that about 15 per cent of all the infected trees in the area 
studied recovered from the disease by the action of these two factors. 
THE PYCNIA AND PYCNOSPORES OF CRONARTIUM RIBICOLA. 
The pycnospores of the Uredinales have received comparatively 
little attention, since it has been generally accepted that they are 
apparently functionless (10, 21, 70, 110, 122, 155). The writer can 
find but little data upon which this idea is based. Plowright (110), 
Thaxter (158), Jaczewski (47), and Klebahn (68) are the only investi- 
gators known to the writer who have actually inoculated plants with 
the pycnospores of their rusts. It seems that the pycnospores should 
be more thoroughly tested. 
The work with pycnospores of Cronartium ribicola in Europe seems 
to be limited to that of Klebahn (68), who made inoculations with them 
upon young Pinus strobus trees without infection occurring. Even 
in this case there was not a clear-cut result, such as is to be desired. 
More recently Colley (18) has shown the importance of the pycnial 
spots, drops, and scars as symptoms of the blister rust in pine bark, 
and still more recently (20) he has investigated their morphology and 
cytology. 
10 Rhoads, A. S. Op. cit. 
11 Pose} 7 , G. B., and Gravatt, G. F. Field studies on the white-pine blister rust at Kittery Point, Me. 
Seen in manuscript. 
