ANATOMY OF A GALL ON POPULUS TRICHOCARPA 
Kart C. Hype 
(WITH PLATE VI) 
Early in the fall of 1919 the writer collected some galls upon the 
twigs of Populus trichocarpa T. and G., caused by Macrophoma 
tumefaciens Shear,’ in Greenough Park, Missoula, Montana. ‘These 
galls were relatively large woody growths, and appeared on the trees 
in great numbers. Within an area of about one acre, at the north 
edge of the park, there were as many as twenty-five trees of various 
sizes bearing galls, while the trees throughout the rest of the park 
were practically free from knots. A close examination of the 
infected trees showed that nearly every twig bore from one to many 
galls, and that above these galls in many cases the twigs were 
gradually dying. The disease, although apparently occurring only 
in isolated localities, appeared to the writer to merit further investi- 
gation, and accordingly the problem was attacked at such an angle 
as to show, if possible, what effect the fungus had upon the normal 
twig to bring about the hypertrophy resulting in the gall. 
Introduction 
Populus trichocarpa is the largest tree of the genus, sometimes 
attaining a height of 65 m. and a diameter of 2.6m. It is a rapid 
grower, and is usually found in the lowlands. It is very common 
throughout the Pacific coast region along the banks of streams, from 
southern Alaska to northern California, extending as far east as the 
ontinental divide in Montana. In Washington, Oregon, and east- 
ern Montana it is the largest of the broad-leaved trees, tending to 
break somewhat the monotony of the vast stretches of coniferous 
forests of the region in its range. The tree is widely used for shade 
and ornament for parkings and lawns of the cities of the northwest. 
In Missoula, for example, there are many trees of this species within 
the limits of the city. It is especially adaptable for regions of light 
t Hupert, E. E., A new Macrophoma on galls of Populus trichocarpa. Phytopath. 
5:182. figs. 3. 19 
Botanical pas vol. 74] [186 
