694 



Journal of Agricultural Research 



Vol. XX, No. 9 



C. fructus developed on the dead outer scale of the bulb, but no evidence 

 of further invasion as occurs with C. circinans was observed. Thus, the 

 two species are distinct as to pathogenicity. 



Measurement of many hundreds of spores of several strains of both 

 species produced on several substrates including the natural ones — 

 namely, apple and onion — showed that the variations due to differences 

 between strains and substrates along with differences due possibly to 

 slight changes in environmental conditions precluded any distinction on 

 this basis. The slight difference in the shape of spores shown in figure 3 

 was quite uniform. The spores of Colletotrichum fructus have walls 

 nearly parallel throughout the middle half, and one end narrows much 

 more abruptly than the other. 



A comparison of growth on potato agar gave further evidence as to 

 the distinction of the two species. The chief points of difference in 

 development on this medium are as follows: (1) Colletotrichum fructus 



Pl G . 3 —spores of Colletotrichum fructus (A) and C. circinans (£). Note the slight difference in shape. 

 In longitudinal section the walls of C. fructus are the more nearly parallel throughout the middle 

 half, while at one end they converge more abruptly. Camera-lucida sketch. X 750. 



grows the more rapidly, (2) appressoria at the tips of hyphae coming in 

 contact with the glass surface in plate cultures are absent in C. fructus, 

 (3) the method of branching is quite distinct — that of C. circinans is 

 dichotomous while that of C. fructus tends to be monopodial in that 

 nearly straight threads of mycelium, which become dark-colored very 

 early and are greater in diameter, run out radially from the center of 

 the colony and send out hyaline side branches of less diameter. Stromata 

 develop at various points from these radial hyphae. This mode of 

 growth gives a somewhat stellate macroscopic appearance to the colony, 

 which differs from that of C. circinans, where distinctly radial hyphae 

 are absent and stromata are scattered. This macroscopic difference is 

 shown in Plate 84. 



Thus, although the morphological characters are only slightly variant, 

 the two forms are considered distinct (1) because of difference in patho- 

 genicity, (2) because of difference in spore shape, and (3) because of 

 difference in type of colony on potato agar. 



