LARCH DISEASES 213 



and may be expected throughout the northern states from 

 the Atlantic to the Pacific. The fungi causing these two dis- 

 eases are closely related to the several other rust fungi of 

 pine, spruce, fir and hemlock. 



Symptoms. 



The rusts of larch are so similar that they cannot be 

 identified without the use of a microscope. The affected 

 needles in early spring show small whitish pustules bursting 

 tlu-ough the epidermis. The epidermis of the leaf covering of 

 the pustules breaks open and the spores within are blown 

 away by the wind as a fine dust. The needles then turn yellow 

 and may fall off. 



Cause. 



The rust diseases of larch are caused by Melampsora 

 Bigelowii and M. Medusm. Besides the stage produced on 

 the larch leaves, each of these fungi requires a period of growth 

 on other kinds of plants. The spores (seciospores) from the 

 pustules caused by the first mentioned species infect the leaves 

 of several kinds of willows. In the latter named species 

 the aeciospores infect the leaves of certain poplars. On the 

 willows and poplars other spores (urediniospores) are produced 

 which continue the life history of the fungi. Over-wintering 

 teliospores on these two hosts germinate in the spring and pro- 

 duce basidiospores which infect the young leaves of the larch. 

 These facts in the life history of the two rust fungi make it 

 evident that the appearance of the diseases on the larch is de- 

 pendent on the presence of poplars or willows in close proximity. 



A blister-rust of larch needles which also occurs rarely in 

 this country is caused by Melampsoridium hetulm (Schum) 

 Arthur. This fungus attacks birch in the United States but 

 the stage on larch does not seem to be common. It is known 

 on both birch and larch in Europe. 



