54 FOREST TREE DISEASES. 



MISTLETOE. 



Our forests have, perhaps, no more widely distributed 

 parasitic enemies than the mistletoes. Two kinds of 

 mistletoes grow on forest trees; one belonging to the 

 genus Phoradendron, an example of which is the ordi- 

 nary Christmas mistletoe, the other belonging to the 

 genus Razoumofskya (Arceuthobium) , and confined to 

 coniferous trees. Phoradendron is the larger of the 

 two and may have leaves, as on oak, or be leafless, as 

 on incense cedar. Its berries are round, white or pink, 

 and contain a seed imbedded in a thick, extremely sticky 

 glue. The seeds are carried by birds from one tree to 

 another, adhere to the bark, and germinate. The 

 Phoradendrons are light-seeking, and therefore grow 

 high up in the tree (PL XXI). Razoumofskya (PI. 

 XXII) is smaller. The thin and brittle stems stand 

 out from the branch they grow on like a small yellow- 

 ish brush. The oval berries hang on erect stems, and 

 are light green in color. In ripening they develop a 

 considerable inside pressure, which increases until the 

 slightest disturbance is enough to make them explode 

 and eject the seed with some force. These are scattered 

 about at random, and many perish for lack of food; 

 others stick to the bark of young branches and twigs 

 and germinate. The Razoumofskya species are more 

 tolerant of shade than the Phoradendrons. 



Mistletoe seeds of both groups can germinate under 

 normal conditions almost anywhere, but they can pene- 

 trate only the young, thin bark of those hosts to which 

 they are adapted. For example, Razoumofskya seeds 



