CURRANT DISEASES 



215 



After the spores escape, a whitish membrane is left about the 

 edges of each pustule (Fig. 57) ; this disappears by the first of 

 June and an empty depression remains. Affected trees are 

 stunted : the tops have a peculiar bunched growth, the past 

 season's growth is 

 shortened, and fi- 

 nally the needles 

 turn yellowish in 

 color. 



Cause of Euro- 

 pean rust. 



This rust fungus, 

 Cronartium Ribicola, 

 like many others, 

 is heteroecious; 

 that is, it requires 

 two distinct kinds 

 of hosts for its full 

 development. And 

 during its life-his- 

 tory five spore- 

 forms are devel- 

 oped. The fungus attacks and lives in the bark of the 

 white pine in one stage of its life-history; as such it is 

 known to scientists as Peridermium Strobi. It may also occur 

 on other five-needle pines, such as the stone-pine (Pinus 

 Cembra), sugar-pine (Pinus Lamberliana) , western white pine 

 (Pinus monticola), and Himalayan white pine (Pinus excelsa). 

 The white pine (Pinus Strobus) is found in North America 

 from Newfoundland to Pennsylvania, along the Appalachians 

 to Georgia, west to eastern Iowa and Minnesota ; in Canada 

 from Lake Winnepeg to the northern shore of the St. Lawrence 

 Gulf and Newfoundland. In the other stage, the fungus lives 

 in the leaves of about twenty-five different species of wild and 



FIG. 56. European currant-rust ; telia on lower 

 surface of black currant leaf. 



