1922] ‘HYDE—GALL ON POPULUS 187 
rainfall because of its long roots and ease of propagation. The roots 
were formerly used by the Indians of California and Oregon in the 
manufacture of hats, baskets, mats, and other ornaments, being well 
adapted for this purpose because of their toughness, fineness, and 
length. The wood is dull brown, with nearly white sapwood, soft, 
light, and weak, with a specific gravity of 0.38. It shrinks moder- 
ately, warps considerably, is easily worked, but is not durable. It 
has a dull silky lustre, and is used extensively for cooperage, boxes, 
tubs, bowls, canoes, wooden legs, and paper pulp. 
The only published work that treats of this gall is that of 
HvuBERT, who deals with the characteristics of the fungus which is 
thought to be the cause of the gall. He originally found the galls 
on twigs of Populus trichocarpa in 1909, and at first thought they 
were caused by an insect, Saperde populnea L. In March 1910 
another collection was made, and he identified the causative organ- 
ism as a species of Macrophoma, but was unable to determine its 
specific identity. In November 1910 he sent samples of the galls to 
C. L. SHEAR, United States Bureau of Plant Industry, who described 
and named the fungus Macrophoma tumefaciens. 
According to HuBERT, the fungus and galls are widely distributed 
throughout Montana on the twigs of Populus trichocarpa. The 
several cities mentioned as localities in which he has observed the 
galls show that they occur at least throughout the western part of 
Montana and the eastern part of Idaho. 
Method 
As the xylem of the normal wood is comparatively soft, no 
difficulty was experienced in obtaining satisfactory sections. 
Sections of the galls were made with a sliding microtome because 
they were more uniform in thickness, and good photomicrographs 
could be secured more readily. First the knots were cut into cubes 
of suitable size for clamping into the microtome. These cubes were 
then placed in a mixture of equal parts of glycerine, alcohol (95 
per cent), and water, and heated for one hour at a temperature of 
100° C. This treatment served the double purpose of softening the 
wood and of removing a considerable amount of air. All of the air, 
however, was not eliminated by this process, and it was necessary 
