10 BULLETIX 1286, U. S. DEPARTMENT OF AGRICULTURE 
center of the smaller spots or around the margins of the larger ones 
on the upper leaf surface, minute black points appear, which repre- 
sent the further fruiting stages of the fungus. (Pis. V and VI.) On 
account of their position around the spots these little stromatic bodies 
often form nearly complete rings, which are very characteristic of 
this disease on full-grown leaves. (PL VI.) 
Young twigs, flowers, fruits, leaf petioles, and fruit stalks are also 
attacked, causing black hypertrophied areas or cankers. 
LIFE HISTORY AND DESCRIPTION OF THE CAUSAL FUNGUS 
The South American leaf disease is caused by the fungus origi- 
nally described as DothideJla ulei P. Hennings (11, p. 134; 12, p. 
254; 20, p. 849; 25, p. 318), of the family Dothideaceae. The dis- 
agreement concerning its taxonomic position has already been men- 
tioned under the review of literature. Since the limits of both 
families, Dothideacese and Sphaeriacese, to which it has been re- 
ferred, are ill-defined and not based sufficiently on the developmental 
morphology of the fruiting bodies, the classification of more or less 
atypical forms, such as the present one, is naturally attended with 
uncertainties. Therefore, until more is known, the writer prefers to 
use the original name. 
DothideJla ulei has three fruiting stages, earlier thought to rep- 
resent different fungi, the identity of which, however, Stahel (23) 
was able to demonstrate beyond reasonable doubt by tracing their 
mycelial connection in the leaf. The first or conidial stage, belong- 
ing probably to the type genus Scolecotrichum, but referred also 
by some authors to the closely similar genera. Fusicladium (IS) and 
Passalora (1) , develops mainly on very young leaves or other 
tender succulent parts as petioles, flowers, flower stalks, and young 
twigs. On account of the great susceptibility of the tissues of these 
organs at this time and the enormous number of conidia which 
are produced, this stage of the fungus is probably entirely respon- 
sible for the rapid spread and destructive defoliation of the trees. 
The conidia are readily carried by the wind from tree to tree. 
According to Stahel (23), who has worked out the method of pene- 
tration and infection, a conidium falling upon a very young leaf, 
for example, germinates and forms an expanded appressorium. 
from which an infection tube penetrates the cuticle and gains en- 
trance to the tissues. Leaves more than a week old are no longer 
susceptible. 
Germination and the successful penetration of the susceptible 
leaf can occur only after moisture has been present continuously 
for 10 to 12 hours, such as happens, for example, on a very dewy 
night. Once inside the leaf the fungus spreads in all directions, and 
after a period of about five days the first external symptoms of the 
disease may be observed. One to two days later conidiophores of 
the "primary Scolecotrichum stage" appear scattered individually 
over the surface, and new conidia are formed. Thus, in less than a 
week the fungus is able to reproduce itself, a fact which explains 
the very rapid spread of the disease under favorable conditions. 
Later, when those young diseased Leaves not killed by the fungus 
have grown further and have acquired their green color, this pri- 
mary stage in which the conidiophores are able to break through 
