DISEASES OF LIME AND OTHER CITRUS TREES 211 



and is probably the species producing these effects on the lemon, 

 there is a considerable weight of opinion at the present time 

 that the fungus in question is mainly saprophytic, and at most 

 a weak parasite of plants or parts otherwise injured or in poor 

 condition. This is the position taken up in recent accounts 

 from Cuba and Porto Rico, and agrees with experience in the 

 Lesser Antilles, where, owing to the absence of the more active 

 fungus, the affection has never been held to be of much account. 

 The fungus appears with great regularity on dead and dying 

 twigs or leaves of citrus trees, even when these have been re- 

 moved from the tree in a healthy condition. It is thus difficult 

 to secure evidence of parasitism, especially as infection experi- 

 ments on healthy material are reported in many cases to have 

 completely failed. 



Symptoms. 



Spots attributed to this fungus occur on leaves in the form of 

 dead brown areas extending often from the tip or margin, in 

 which develop numerous small dark pustules of the fungus, often 

 arranged concentrically. The inj ury appears usually on senescent 

 leaves or as a consequence of insect injuries. 



On the fruits the fungus is found occupying hardened brown 

 spots or large brown to blackish blotches up to an inch or two in 

 diameter on the rind ; these are generally somewhat sunken, and 

 are situated in any position. As a rule only a few isolated 

 spots occur in the produce of any particular tree, and usually they 

 can be attributed to some predisposing injury. On trees which 

 are suffering from the general effects of some serious disease, how- 

 ever, a large percentage of fruit may be attacked by anthracnose. 

 Tear-streaking of the rind is attributed to the effect of the ger- 

 mination of spores washed down in quantity from dead twigs. 



In the great majority of cases the fungus as it occurs on the 

 twigs appears to be entirely saprophytic ; in a few instances 

 which have come under the writer's observation it has assumed 

 the aspect of a parasite on twigs of which the resistance has been 

 lowered by external conditions. 



Fungus. 



The fungus in its common Gloeosporium condition is difficult 

 to distinguish from G. limetticolum, in comparison with which its 

 characters are discussed (page 208). On dead twigs fringes of 

 dark setae may be produced around the pustules, which then 

 appear as black dots to the naked eye. Setse have not been ob- 

 served in the lime parasite. 



Control. 



The position of the fungus as a weak parasite able to attack 

 only injured or debihtated parts indicates the nature of the 

 remedies to be applied where its effects are regarded as serious. 



