SPRUCE DISEASES 



323 



The mistletoe plant is very small. It is usually less than a 

 half inch tall but may grow as large as one inch. The pollen 

 and seed are produced 

 on separate plants which 

 usually grow on different 

 trees. The plants con- 

 sist of a short stem 

 with appressed scale-like 

 leaves. They are either 

 yellowish or dark colored. 



Cavse. 



The witches'-broom of 

 spruce is caused by the 

 dwarf mistletoe, Ra- 

 zoumofskya pusilla. The 

 floral organs of the plant 

 are matiu-e in early spring 

 and the seeds are ready 

 to be disseminated in 

 September. Before the 

 seeds are discharged, the 

 plants bend toward the 

 tip of the branch. In 

 this position the seeds 

 are forcibly projected and 

 being sticky they adhere 

 to the younger twigs on 

 which they may lodge. 

 Rootlets are sent into 



the bark and wood of Fig. 63. — Mistletoe witches'-brooms on 



the twig and a parasitic black spruce. Tree almost dead. 



relation established. The increased growth of the branches 

 and the formation of the witches'-brooms are due to the 



