148 



spots were counted on a square centimetre of a badly infected leaf and-' 

 44 spots on a square centimetre of one slightly infected. In the grape 

 fruit only 130 spots to the square centimetre were found on a badly 

 infected leaf ; these were partly confluent, forming an almost continu- 

 ous blotch. Where the spots are very abundant, they frequently 

 run together, forming large, irregular, dark brown blotches. This 

 frequently occurs on all species of citrus trees affected with the disease, 

 and is found on stems, leaves, and fruits. On the fruits in particular 

 this is of frequent occurrence. As the fruit ripens, the blotches, which 

 are hard and brittle, sometimes become considerably checkered and 

 fissured, similar to the cracking of mud in drying. 



The spots are to some extent formed on both surfaces of the leaf, but 

 are much more abundant on the upper surface. This character is more 

 particularly noticeable in the grape fruit than in other species of cit- 

 rus. On grape fruit the spots are almost wholly limited to the upper 

 surface. In the common sweet orange and sour orange they occur 

 abundantly on the lower surface, but are still more numerous on tbe up- 

 per surface. On the different portions of the fruit and young stems the 

 spots are apparently uniformly abundant. This malady is most 

 severe on the lower portions of the tree, but the characteristic spots 

 are also found on the leaves and twigs in the tops of large trees, nearly 

 30 feet from the ground. 



The infection, it appears, usually takes place at an early stage in the 

 development of the leaves and stems, and if the disease becomes severe 

 the affected organs are considerably modified in appearance. The 

 leaves become greatly distorted and wrinkled and remain much smaller 

 and more pointed than normally. Many of the leaves fall before reach- 

 ing matuiity, only a scanty foliage remaining on badly affected 

 branches, The branches are also considerably contorted and stunted 

 in severe attacks. 



Cause. — From studies that have been made of this disease it seems 

 very probable that it is caused by some vegetable parasite, although the 

 microscopic studies which have thus far been carried on have failed to 

 reveal the presence of any such organism. The disease is apparently 

 contagious, spreading from definite centres. In some groves infected 

 areas are plainly seen. In the centres of these areas, where the disease 

 first started, the trees will be found to be very badly affected, but 

 toward the margins the malady gradually becomes less apparent. 



Melanose appears to be of an entirely local nature. In its growth 

 and development each spot is entirely independent of any other spot,, 

 probably being caused by a separate infection. The tissue between, 

 the diseased spots is evidently perfectly healthy outside of the gen- 

 eral debility which results from the infection of such a large portion 

 of the leaf. The strict localization of the disease, so similar to what 

 occurs in scab, again strongly suggests that the disease is caused by 

 some vegetable parasite. Infection can take place apparently only 

 when the tissues are quite young. If the leaves and stems escape the 

 disease until they are nearly full grown the danger of infection is past^ 

 This is the case also with fruits, ard therefore spraying to prevent the 

 disease must be done early, while the fruits are small. After they 

 reach an inch in diameter they appear to be safe from infection and^ 

 spraying may then be discontinued. 



