74 BULLETIN 1380, TJ. S. DEPARTMENT OF AGRICULTURE 
may be elongated or hemispherical in shape (PL XXXIII). Their 
structure, however, may tend to increase their bulk. Instead of being 
of solid clear rubber their internal appearance is that of a black 
rubber sponge, with the exception that the cavities are usually 
elongated and tend to radiate from the base. These cavities are 
apparently inhabited by the insect, since cocoons of a brown sub- 
stance were found in them. The surface of the pads appears to be 
made up of gelatinous granules resembling the excrement of some 
insects. 
A fungus, Dendrographium atrum, was always found growing 
on the surface of these pads. This species forms short, black, stiff 
hairlike stalks which consist of bundles of septate hypnae. On the 
free ends of the hyphse multicellular dark-colored conidia are pro- 
duced in chains. These stalks are frequently so abundant on the 
pads as to give them the appearance of a fuzzy ball. What relation 
the fungus has to the structure and formation of the pads is un- 
known. Various blue-black molds were also present, different from 
those usually found on crude rubber. 
An injurious effect seemed to accompany the development of these 
pads, in that the cuts supporting them were not healed and were 
frequently of a cancerous nature, with much discoloration of the sur- 
rounding tissues. 
CHLOROSIS OF LEAVES 
Mention has already been made of a sclerotic condition of Hevea 
leaves in connection with an indeterminate leaf disease. Chlorosis 
without fungus association was not uncommon on leaves of young 
trees growing in dry sandy soil. The yellowing of the leaves was 
either uniform over the surface or appeared as irregular areas and 
sometimes bounded by the larger lateral veins. 
Chlorosis occurred in two forms. In one the epidermis on the 
upper side of the leaf only was affected, causing an opaque condition 
when the leaf is held to the light. In the other the yellow spots were 
translucent to transmitted light, and they were apparent from both 
sides of the leaf. 
No fungi or insects were found on chlorotic leaves, although the 
condition could be caused by the latter. The condition sometimes is 
known to be induced by root-rot and insufficient nourishment, but it 
was not possible under the circumstances to determine that point. 
ABNORMAL GROWTHS AND CONDITIONS 
SPIRAL TRUNK 
The widely observed spiral, twisted, or screw growth of the surface 
of trunks so common on conifers and frondose trees in the Temperate 
Zone was noticed in a small even-surfaced Hevea standing in damp 
soil on the Rio Solimoes. In this case the phenomenon was quite 
conspicuous, the spiral line of growth making one complete turn 
within the space of 2 feet of the longitudinal axis of the trunk. This 
phenomenon has not been very satisfactorily explained. It is some- 
times considered to be the result of the departure of the cambial cells 
in their line of growth from the vertical, causing the wood to be 
laid down at an angle to the longitudinal axis of the trunk. 
