RUBBER (HEVEA) DISEASES 37 
appear singly or in clusters of three or four and may be on either 
side of the leaf. Pycnidia and perithecia may occur together on the 
same spot, or pycnidial cavities may be contained in the same stro- 
mata with the perithecia. This is a rare condition, however, and 
when pycnidia are present they may be distinguished in a section of 
the stroma by their size and shape. Evidence of the occurrence of 
conidia was found by Stahel on the original material studied by 
Hennings. The old leaves may sometimes be very heavily infected, 
and when in this condition they are very rough when drawn through 
the hand. The ascospore stage was common in the Amazon Valley 
and was the only stage found in some localities where the trees were 
of a uniform size with little variation in the age class of the leaves. 
The production of the ascospores is evidently continuous at all sea- 
sons of the year and probably plays a greater role in the propagation 
of the fungus than has heretofore been believed. The spores are 
capable of germination immediately after their expulsion from the 
ascus. They may be carried by the wind, rain, or insects to the young 
leaves and give rise to the first or conidial stage. 
Stahel's experiments with ascospores showed that they did not 
withstand drying for more than 4 to 6 hours. They germinated in 
water in about 2 hours. He sowed the spores on young leaves in a 
damp chamber and found it required about 16 hours for the germ tube 
to penetrate the leaf partially. It appears that the disease has not 
been experimentally reproduced by means of ascospores sown on 
young leaves under normal conditions. One infection resulting in 
the production of conidia was obtained at Para by inoculating with 
ascospores young folded leaves which had been protected from spu- 
rious infection with transparent oiled-paper bags. Four different 
buds were inoculated and again inclosed in the bags. Infection oc- 
curred at the end of one week. This result is far from conclusive 
and is open to many objections, but there was no opportunity for 
more critical work. All the evidence heretofore presented on the 
relationship of the different stages appears to be based on anatomical 
studies by tracing the mycelial connections in the leaf. It is highly 
desirable to establish the life history of the organism by extended 
and critically controlled experiments under natural conditions. 
All three spore forms occur on leaves, petioles, young stems, in- 
florescence, and fruits (PI. XV, A to E). On the petioles and stems 
the infections are at first noticeable as slightly elevated greenish or 
yellowish areas. These soon become black, the surface tissues crack 
open, the bast is hypertrophied, and definite, though small, cankers 
are formed. Cankered stems bearing perithecia and terminating 
in well-developed young leaf clusters were frequently observed. 
The longevity of the mycelium in the stems has apparently not been 
demonstrated. Cankers on 3-year-old stems were found to have 
abundant fertile perithecia. Cankers were found on older stems. 
but the perithecial stroma had deteriorated and no ascospores were 
found. In case the branch survives the infections it is not likely that 
a viable mycelium capable of producing perithecia survives after 
three years. Infection of inflorescences soon resulted in a shrivel- 
ing and curling of the smaller parts and the falling of the flowers. 
Young vigorously developing fruits in the neighborhood of Para 
were found infected. The necrosis is very striking. Small elevations 
