474 



CITRUS FRUITS AND THEIR CULTURE. 



Fig. 101. S'pore ana spore-bearing- parts of 



leaf-spot fungus. B, spore-bearing- branches. 



A, spores. 



lowing description of the disease will assist in recognizing 

 it : Large, some- 



what circular, 

 yellowish spots 

 are noticed on 

 the leaves. Close 

 examination re- 

 veals the pres- 

 ence of minute 

 dark dots scat- 

 tered thickly 

 over the discol- 

 o r e d areas. 

 These small, 

 dark spots con- 

 tain the spores 

 of a parasitic fungus, which is the cause of the trouble. 

 The sporules are borne on short filaments which are con- 

 tained in the brownish-black conceptacles. Fig. 101 shows 

 some of these conidia and basidia, greatly enlarged. 



This fungus has been known under two different 

 names. It was described as Phyllosticta adusta E. & M. 

 from the specimens collected by Dr. Martin. Later it was 

 referred to the genus Coll&totrichum and named (7. adust- 

 um E. It appears, however, to be identical with Oolleto 

 trichum gloeosporioides Penz. 



More recently, Rolfs has demonstrated that two or 

 three diseases, hitherto not investigated, are caused by the 

 same fungus. It is responsible for the dying back of the 

 twigs of citrus trees, for the death of the blossoms of the 

 lime, for the anthracnose of the lime and the black-spot 

 disease on the rind of the lemon.* 



* More recently the author has investigated a serious disease of 

 pomelo fruit caused by the same organism. 



