FUNGI AFFECTING SHADE TREES 



The Catalpa Leaf=spot Disease 



Pliyllosticta catalpce 



Early in summer small discolored spots frequently 

 appear in the leaves of Catalpa trees. Although minute 

 at first they gradually enlarge, and tvvo or more often 

 run together to form brown or blackish blotches^ which 

 sometimes inyolve most of the leaf. In badly affected 

 trees the tissues of the leaves may be so diseased as to 

 cause defoliation during the latter part of summer. In 

 less severe cases the affected areas may drop out of the 

 leaves, round holes appearing in their stead. 



This disease is caused by a fungus which originates 

 in spores like those represented in Fig. 51, i. When 

 one of these spores falls upon a moist catalpa leaf it ger- 

 minates by sending out tubes, as illustrated in c, of the 

 same figure, and these germ tubes enter the leaf-tissues, 

 W'here they develop a mass of mycelium, which grows at 

 the expense of the leaf cells, the latter becoming disor- 

 ganized and turning brown. After the mycelium has 

 developed in this way for some time it produces spores 

 in certain parts of the spot, rupturing the skin, or cuti- 

 cle, of the leaf, to enable the spores to escape, as shown 

 in a. These spores are blown or washed upon other 

 leaves where, under favorable conditions, they may ger- 

 minate and start new spots. There is another fungus, 

 quite different in microscopic characters from the one 

 illustrated, usually found on the spots, but it is believed 

 to be a secondary form growdng on the disorganized 



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