Minnesota Plant Diseases. 281 



clustered that the so-called broom looks like a foreign bush 

 growing on the spruce tree. In badly infected trees the 

 whole plant may consist of bunches of these brooms. By 

 the death of the lower broom-branches, the tree may be left 

 with only a few brooms remaining at the top. The symmetry 

 of the tree is therefore entirely destroyed and the natural 

 growth is very seriously interfered with. Whole forests in Ot- 

 tertail and Becker counties are badly infested so that in many 

 cases a majority of the trees are diseased. It has also been re- 

 ported from Itasca county. In view of the decline of the pine 

 forests and the growing importance of the spruce, this disease 

 will later prove of very serious consequence. It is not appar- 

 ently common on the north shore of Lake Superior but will 

 probably reach all of the spruce-growing regions of the state in 

 the course of time unless measures are taken to prevent it. 



The parasitic plant is very small, seldom an inch in length, 

 and its parasitic habit has greatly affected its structure. The 

 leaves are reduced to mere scales and the very short stem is 

 reddish or only slightly greenish. It is rooted in the branches 

 of the spruce tree from which it derives its nutrition. Many 

 plants often arise from the terminal region of a single spruce 

 branch. The flowers are very much reduced in structure and 

 are of two kinds, staminate and pistillate, growing on separate 

 plants. The seeds are produced in berry-like fruits and are 

 provided with sticky envelopes by means of which they cling to 

 the branches of the trees. They are probably distributed by 

 birds. 



The only known remedy is the destruction of the infected 

 trees, which will prevent the spread of the disease. This can 

 easily be effected when the trees are bad'y diseased for the lat- 

 ter can be readily recognized by the brooms and the general 

 irregularity of growth. Care should be taken to find those in 

 the early stages of infection for such trees have not yet devel- 

 oped conspicuous brooms and may still harbor the parasite and 

 thus become the center for new infections to the neighboring 

 trees. (See Figs. 24, 25, loi.) 



Downy mildew of seedling trees{Phytophthora omnivora De 

 Bary). See Diseases of Greenhouse and Ornamental Plants. 



