28 
The Colorado Experiment Station 
On the leaves we find reddish or blackened areas developing 
along the large veins on the under surface. The veins may be eaten 
thru by the fungus and destroyed, while the blade shows numerous 
cracks or holes with shriveled, blackened margins. Leaves in this 
condition are practically worthless as food-building organs, and as a 
result the nutrition of the plant is greatly impaired; either the yield 
of seed is reduced appreciably or the seed fails to mature. 
Previous to the time of blossoming, the attack has been concenr- 
trated against the leaves, and by the time the young pods make their 
appearance the fungus has become well established and is amply sup¬ 
plied with spores. These soon find their way to the young, tender 
pods where they produce rusty-brown or black sunken spots with 
reddish or yellowish margins. (See Fig. III.) These vary in size, 
much as the bacterial spots previously described. The spores of the 
fungus are produced in the center of the black ulcers and form little 
pink masses visible to the naked eye. They are glued together with a 
mucilaginous material which sticks them securely to the spot. How¬ 
ever, as soon as a drop of moisture touches them, the mucilage is dis¬ 
solved and the spores are set free in the water. At this time any 
disturbance of the plant is apt to scatter the spores in the flying drop 
of water, and for this reason beans affected with anthracnose should 
never be cultivated while the dew is on them or while they are wet 
from a shower. 
From the affected pods, the disease finds its way to the seed 
where it produces the familiar rusty-red or brown spots. In severe 
cases, the whole seed may be involved, altho ordinarily only a slight 
discoloration is produced on one side. 
Bean Rust 
Bean rust was observed in several fields last year, but it came 
so late in the season that little if any damage resulted. The causal 
fungus, Uromyces appendiculatus, attacks the leaves, stems and pods. 
The rust, as the name implies, can 'be recognized in its summer stage 
by the small, raised, rusty-brown powdery specks on the under side 
of the leaf which rub off easily with the fingers as a rusty-brown 
powder. 
* 
In the winter stage, the specks are black in color and occur on 
"both surfaces of the leaf. When found on the upper side, they are 
usually surrounded by a light border, apparently where the green leaf 
tissue has been killed. (See Fig. IV.) While the rust is not uncom¬ 
mon, it has rarely been of sufficient economic importance to cause any 
considerable alarm. Of course, if the attack should come early in 
the season and be very general, the crop would suffer in proportion as 
