104 



note that we have been able to find in American publications.* 

 It is strange that so important a disease, and one so widely spread 

 as this seems to be in this country, should have attracted so little 

 attention here. In Europe, however, the disease has been very 

 carefully studied and excellent accounts of it have been published. 

 The most complete one that we have found is that given by 

 Sorauer in his great work on the diseases of plants. J 



Symptoms o! the Disease. — Burrill and others state that when 

 the young leaves appear in the spring or during the summer, red- 

 dish spots an eighth of an inch or more in diameter may be seen 

 scattered more or less numerously over their surface ; that these 

 spots are especially conspicuous on the upper side of the leaves ; 

 but that at a later tim2 the spots turn brown by the death of the 

 parts, after which they are more easily discovered beneath. 



Karl}- in August, 

 when we began oui 

 studies of the dis- 

 ease on some bad- 

 ly infested trees, 

 no reddish spots 

 were observed. 

 The diseased parts 

 were brownish or 

 black, and had a 

 corky appearance. 

 These spots occur 

 either singly scat- 

 tered over the sur- 

 face of the leaves, 

 or are massed so as 



to form large 

 Fig. \. — Cluster of infested leaves, a Upper surface , - - , . , f 



ofleaf; b lower surface ; c huo galls enlarged. Dlotcnes wnicn OI- 



ten involve a large part of the leaf. (Fig. i). 



If these spots be examined from the lower side of the leaf with 

 a microscope of low power, a good hand lens is sufficient, there 



*Mr. H. Garman has published an excellent article on the general sub- 

 ject of the Phytopti and other Injurious Plant Mites in which there is a 

 brief description of Phytoptus pyri by Professor Burrill, Twelfth Report of 

 the State Entomologist of Illinois, (1S83), p. 123-143. 



fDr. Paul Sorauer, Handbuch der Pflanzenkrankheiten, Erster Theil, s. 

 814-825. 



