Minnesota Plant Diseases. 



53 



ual, it is living parasitically on the remainder of the host plant. 

 That the broom itself is not injured, but rather stimulated, in 

 its growth is seen by the production of such numerous and 

 large-sized branches. But the ultimate effect upon the whole 



I'IG. 13. Witches'-broom on balsam fir, caused by a rust fungus (. \ecidium rla(imiin). 

 The branches of the broom arc vertical instead of horizontal, as are the normal, un- 

 diseascd branches in the ni;ht of the picture. <hiiMti.il. 



plant is injurious because the normal balance of nutrition and 

 work has been interfered with for the rapid production of a 

 group of larger but worthless branches. In a word, therefore, 

 the witches'-broom mav be described as a bush- or broom-like 



