PARASITISM OF COMANDRA UMBELLATA 
By George Grant Hedgcock, 
Pathologist, Investigations in Forest Pathology, 
Bureau of Plant Industry 
One of the most important and most injurious of the stem or blister 
rusts occurring on pines is Peridermium pyriforme Peck, which attacks 
Pinus (murrayana)contorta Loud., P. ponderosa Laws., and P. ponderosa 
scopulorum Engelm. in the western United States, P. divaricata Du Mont 
de Cours. in the Northern States, and P. pungens Michx. and P. rigida Mill, 
in the Northwestern States. Peridermium pyriforme is a hetercecious 
rust and is dependent for its existence upon its alternate, or summer, 
stage, which occurs on species of Comandra. 
The problem of the eradication of this important rust being so inti¬ 
mately associated with plants of Comandra spp. led the writer to investi¬ 
gate their manner of growth and means of propagation. It was found 
that the plants of at least two species, C. pallida A. DC. and C. umbellata 
(L.) Nutt., have apparently become largely dependent on parasitism 
for their continued existence. The other two North American species, 
C. livida Richards, and C. richardsiana Femald, resemble the former 
species in appearance and habit and are probably equally parasitic in 
their nature. 
The writer has carefully examined the root system of living plants of 
both C. umbellata and C. pallida , but only of dried specimens of the other 
two species. The former have long underground rootstocks which bear 
here and there small roots or rootlets usually less than 5 inches in length. 
These rootlets branch sparsely and are nearly always attached to the 
roots or underground stems of other species of plants. At the point of 
attachment there is formed by the root of Comandra spp. a nearly hemi¬ 
spherical disk or holdfast. This holdfast is either superficial or slightly 
embedded in the cambium layer of tissues of the host, but does not send 
out haustoria, as is the case in species of Razoumofskva on the limbs 
and trunks of coniferous trees. The chief function of the roots of 
Comandra spp. appears to be that of attachment to host plants for the 
purpose of obtaining nourishment and a water supply. Plants of Coman- 
dra spp. frequent dry, rocky soils, which often have a low water content. 
Plants of all these species of Comandra bear leaves; and although 
attached as parasites to the roots of other plants, they are not entirely 
dependent upon their host plants for organic compounds, since they are 
able to further elaborate these compounds in the liquids received from 
Journal of Agricultural Rsearch. 
Dept, of Agriculture, Washington, D. C. 
Vol. V, No. 3 
Oct. 18, 1915 
G—60 
