4 BULLETIN 28, PORTO RICO EXPERIMENT STATION. 
The disease is characterized by the occurrence on the leaves of small spots 
usually circular in outline, but sometimes ovoid along the veins. The newer 
ones are very dark, the older ones light colored. The spots are usually about 6 
millimeters in diameter, although many of the older ones become 12 to 13 milli- 
meters in diameter. Sometimes they fuse or give entrance to other tissue- 
destroying fungi which infect the intervening tissue, producing spots of consid- 
erable size. The worst affected leaves have from 30 to 40 or even more spots, 
so that a large proportion of the leaf tissue is destroyed. On the upper surface 
of many of the spots and also to some extent on the lower surface may be seen 
hairlike projections from 1 to 4 millimeters long of a yellowish color, each bear- 
ing at the end a head so that they resemble minute pins. This is the reproduc- 
tive or fruiting stage of the fungus. Each spot produces a continuous crop of 
these hairs so long as weather conditions are favorable. The total number at 
any time is small, and in an entire season but from 20 to 50 are produced in 
each spot, judging from the number of old filament bases. The largest number 
observed was 70 in a spot of 7 millimeters diameter. As the leaf spots become 
older, growth having stopped for any reason, such as the advent of the dry 
season, the diseased tissue falls away, leaving numerous circular openings in the 
leaf. In other leaf diseases the dead tissue remains. 
Sometimes the fungus attacks young stems, where it causes conspicuous scars 
and so weakens the points affected that they are easily broken by the wind. The 
berries also are attacked, a slight discoloration of the grain being frequently 
caused. 
The microscope shows the filaments, which are solid, not hollow, as sometimes 
stated, to be made up of the fine fungus threads which are somewhat branched 
in the upper part to form the head. The ends of the threads are swollen and 
have sometimes been mistaken for spores when seen in cross section, and de- 
scribed as such. No real spores have ever been found in any of the numerous 
specimens examined. The fungus is distributed by the heads at the ends of the 
filaments being caught by the wind or raindrops and carried to near-by leaves, 
a process facilitated by the heads becoming loosened in the older filaments 
through the formation of cavities or " lacunae " near the point of attachment. 
The head is soon fastened to the leaf on which it happens to fall by the 
numerous threads which it sends out at the point of contact. Within less than 
a week a dark circular spot is formed and new filaments appear, and new loosely 
attached heads are formed on these by means of which the spread of the disease 
is continued. Apparently this fungus has no other way of propagating itself, 
and the writer has not found any other stage of Stilbella flavida, all inocula- 
tions into coffee with suspected forms resulting negatively. * * * 
The injury to the trees is not so much in the actual amount of the leaf tissue 
destroyed, although this may amount to one-fifth or even more of the entire 
amount of the worst cases, but in the defoliations which take place after a 
time. The diseased leaves drop sooner than those not affected, and owing to 
the weakened condition of the tree are not soon replaced. After the first severe 
attack the base of each tree may be seen to be surrounded by a pile of green 
leaves several inches deep. The disease never kills the trees. They live on 
with scanty foliage and are able to put forth some new growth and bear a 
small amount of berries each year. 
The decrease in yield following an attack of the leaf spot is marked. In one 
experimental plat, where a record of the yield had been kept for some years, 
it was found to be 75 per cent. In this case the difference between the trees 
before and after the attack was such as accompanies the loss of the greater part 
of the foliage. * * * 
