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. ponder osa Laws., and P. ponderosa 

 scopulorum Engelm. in the western United States, P. divaricata Du Mont 

 de Cours. in the Northern States, and P. pungetis Michx. and P. rigida MiU. 

 in the Northwestern States. Peridermium pyriforme is a heteroecious 

 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, i-esemble 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 Razoumofskya 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 dr\', 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 Aricultural Rsearch. Vol. V, No. 3 



Dept. of Agriculture, Washington, D. C. Oct. 18, 1915 



ag G— 60 



