XII. SEED DISSEMINATION AND DISTRIBUTION 

 OF RAZOUMOFSKYA ROBUSTA (Engelm.) Kuntze.* 



D. T. MACDOUGAL. 



The branches of the bull pine (Pt'nus ponderosa scopulorum), 

 of the southwestern United States, offer suitable conditions of 

 nourishment for the growth of Razoumofskya robusta, a parasite 

 belonging to the Loranthaceas. Some of the members of this 

 family, such as the mistletoe (Phoradendron flavescens}, which 

 live on deciduous trees in temperate latitudes, are furnished with 

 a fair amount of chlorophyll. These forms are able to carry on 

 more or less food-formation during the warmer portions of the 

 season in which the deciduous hosts lack leaves. Razoumofskya, 

 however, fastens on an evergreen conifer, and hence has no such 

 need or use for chlorophyll. It is, therefore, furnished with this 

 substance in minute quantity only, and its leaves are reduced to 

 mere bracts. It is dioecious, and the aerial shoots of both kinds 

 may appear in close contiguity on the same branch of the host 

 or be separated some distance. The shoots start up from the 

 submerged rhizomes in the latter part of April or early in May, 

 the flowers maturing in June and the seeds in August. After 

 the dispersal of the seeds the aerial portion of the plant dies away, 

 leaving only the haustorial rhizomes buried in the tissues of the 

 host plant. With the opening of the next season shoots are 

 produced as before. 



The submerged portion of the parasite penetrates the branches 

 of the host long distances longitudinally, and where aerial shoots 

 are given off the tissues of the host show abnormal structures, 

 the branches undergoing enlargement, while the development 

 of the nearest buds is variously checked and altered. The dis- 

 tortion is magnified with age, and old trees exhibit the most 

 grotesque malformations. The writer has seen trees a meter in 

 height infected, and the size of the older branches bearing the 



*An abstract of this paper was read before the Botanical Club of the A.A.A.S. 

 at Boston, August 25, 1898. 



