24 BULLETIN 121, U. S. DEPARTMENT OF AGRICULTURE. 



RELATION TO OTHER ANTHRACNOSE FUNGI. 



Upon the basis of Edgerton's theory of species determination by 

 host range, it is of interest to note the reaction of anthracnose fungi 

 from other than cucurbitaceous hosts to the latter. Using the fungus 

 •from bean Frank (19) failed to infect a cucumber fruit and C. O. 

 Smith (9) secured no infection of plants in the cases of cucumber, 

 pumpkin, squash, muskmelon, and watermelon. Likewise, Edger- 

 ton (13) was unable to obtain infection with the bean fungus upon 

 cucumber plants and fruit, and Kriiger (28, p. 246, 294) was unable 

 to infect cucumbers with the fungus from bean. Shear and Wood (45) 

 were also unsuccessful in their inoculations of watermelon, squash, 

 and pumpkin fruits with the bean fungus, but were successful in 

 their inoculations of the fruits of watermelon, squash, and pumpkin 

 with the anthracnose fungus from grapes and also in their inocula- 

 tions of watermelon and pumpkin fruits with the fungus from guava. 

 Halsted (23) secured infection of a citron fruit with the fungus from 

 bean. 



It will be noted that in no case did the anthracnose fungus from 

 another host infect cucurbitaceous plants. In cases of fruit infection 

 it must be borne in mind that the fruit to some extent resembles a 

 nonliving substratum and that successful fruit infection is not proof of 

 active parasitism. 



In the course of the present work, atomizer inoculations of cucum- 

 ber plants in the field with spore suspensions from cultures of bean, 

 cotton, banana, and fig anthracnoses yielded only negative results. 



There seems to be no positive evidence that fungi causing anthrac- 

 nose of hosts other than cucurbits are physiologically identical with 

 the form under consideration, and, as was noted in the consideration 

 of the pathogenicity of ColletotricJium lagenarium, this fungus causes 

 anthracnose of cucurbits only. 



RELATION OF THE FUNGUS TO THE HOST TISSUE. 



Concerning the relation of the fungus to the host tissue, attention 

 has been chiefly focused upon the mode of penetration of the host 

 epidermis and the effect of the advancing mycelium upon the host 

 cells. 



PENETRATION. 



• To determine the method of host penetration, drops of spore sus- 

 pensions were placed in ink circles on leaves of cucumber plants in 

 the greenhouse, and at intervals thereafter these inoculated leaf areas 

 were cut out with scissors, fixed in 10 per cent HC1, and cleared by 

 storing in a saturated solution of chloral hydrate. This was followed 

 by clearing in 3 per cent KOH, and in some cases staining in Dela- 

 field's hsematoxylin. Glycerin mounts were made and the surface of 

 the epidermis was carefully examined under the microscope. 



