12 



the ultimate cause of the disease. The observations of this 

 author indicate that aphids may sometimes be responsible 

 for the occurrence of the trouble in the seed bed and its subse- 

 quent spread in the field. He has succeeded in keeping the 

 disease under complete control in the greenhouse by frequent 

 fumigations to exclude aphids. 



In some of the instances cited the conclusion that insects 

 play a part in the dissemination of these organisms was based 

 merely upon circumstantial evidence. However, in a sufficient 

 number of them enough substantial experimental evidence was 

 presented to point to the importance of insects as carriers of 

 fungous spores and of bacteria parasitic upon plants. 



We may next consider the literature bearing upon the re- 

 lation of insects to the spread of the chestnut blight, or bark 

 disease, caused by the fungus, Endothia parasitica (Murr.) A. 

 and A. From the very beginning of the study of this disease 

 insects have received a good share of the blame for its spread. 

 In 1906 Murrill (38) stated that from the numerous yellowish- 

 brown pustules produced by the blight, "millions of minute 

 summer spores emerge from day to day in elongated reddish- 

 brown masses, to be disseminated by the wind and other 

 agencies, such as insects, birds, squirrels, etc." Later in the 

 same publication he added that "every bird and insect that 

 rests upon an infected spot is liable to carry the spores upon 

 its feet or body to other trees." 



Several years later Hodson (22) said that "the spores are 

 no doubt carried by animals, birds, insects, and by the ship- 

 ment of infected material," The statement is made by Metcalf 

 and Collins (37) that "there is strong evidence that the spores 

 are spread extensively by birds, especially woodpeckers, and 

 there is also excellent evidence that they are spread by insects 

 and by various rodents, such as squirrels." Ah essentially 

 similar statement was made the following year by Metcalf (36). 



In discussing the methods by which conidia are transported 

 from one tree to another, Rankin (39) makes the following 

 statement: "Reasoning by analogy with what is known of the 

 behavior of many fungi, such agencies as borers, birds, ants 

 and the wind, etc., have been suggested but in no wise proved 

 to be responsible." 



