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A New Leaf Spot of Viola Cucullata. 



H. W. Anderson. 



A leaf spot on Viola cucullata has been prevalent in Indiana and 

 neighboring States for a number of years. It is especially noticeable dur- 

 ing the early spring months. Collections of leaf spots on this host in 

 different parts of the country have been made from time to time and have 

 been filed away in the herbarium without being classified or wrongly labeled 

 as the Phyllosticta leaf spot. A careful examination during the past year 

 has revealed the fact that this particular leaf spot is caused by a Colleto- 

 trichum which has never been described as occurring on this species. Since 

 this disease is widespread it was thought worth while to make a careful 

 study of the causative organism. 



Of the violets which occur in this region only Viola cucullata has been 

 found to be attacked by this particular fungus. It is interesting to note 

 that while this species is attacked V. palmata is apparently immune. 

 V. cucullata was formerly considered a variety of V. palmata and the im- 

 munity of the latter emphasizes the specific difference. However, only a 

 limited number of plants of T 7 . palmata have been observed and these in a 

 region where the disease was not common on the other species. 



Cultivated violets have been examined only in the local greenhouses. 

 It is probable, however, that all cultivated species are immune, otherwise 

 the disease would have been observed and reported by those especially 

 interested in violet diseases. 



Macroscopical Appearance. — The fungus produces a typical leaf spot. 

 The earliest indication of infection is a pale area with a definite dark 

 green border. Later the area in the center of the spot dies, turns white, 

 grey or light brown, a dark brown ring appears about the edge, forming a 

 definite, regular spot. At an early stage the acervuli appear as dark brown 

 dots on the lighter central area. They are irregularly arranged and occur 

 on both sides of the leaf. The dark color of the acervuli is due, in part, to 

 the numerous setae. Later the center of the spot becomes very thin and 

 papery and may fall out, thus giving a shot hole effect. When badly in- 



