398 



RESEARCHES ON FUNGI 



The American Coffee-leaf disease, as it occurs in Porto Rico, has 

 been thus described by Fawcett.^ " The disease is characterised by 

 the occurrence on the leaves of small spots usually circular in outline, 

 but sometimes ovate along the veins. The newer ones are very 



, „ _„ dark, the older ones 



•^■-^ light colored. The 



"^ spots are usually 



^'^ about 6 mm. in 



diameter, although 

 many of the older 

 ones become 12 to 

 13 mm. in diameter. 

 Sometimes they fuse 

 or give entrance to 

 other tissue-destroy- 

 ing fungi which 

 infect the interven- 

 ing tissue, producing 

 spots of considerable 

 size. The worst 

 affected leaves have 

 from 30 to 40 or 

 even more spots, so 

 that a large propor- 

 tion of the leaf tissue 

 is destroyed. On 

 the upper surface of 

 many of the spots 

 and also to some 

 extent on the lower 

 surface may be seen 

 hair-like projections from 1 to 4 mm. long of a yellowish color, each 

 bearing at the end a head so that they resemble minute pins. This is 

 the reproductive or fruiting stage of the fungus [cf. Figs. 201 and 202, 

 pp. 402 and 403]. Each spot produces a continuous crop of these 

 hairs so long as weather conditions are favourable. The total 



1 G. L. Fawcett, loc. ciL, pp. 11-12. 



Fig. 198. — A Coffee tree almost defoliated by Omphalia 

 fldvida. Only tlie youngest leaves remain on the 

 twigs. Photographed by G. L. Fawcett at the 

 Mayagiiez Experiment Station, Porto Rico. 



