56 [ DISEASES OF CITRUS TREES 



This is only a physiological process, but may become 

 pathological when a sudden heat wave in May or June 

 deprives the tree of all its fruit, or when without any 

 apparent cause the fruit is shed off almost entirely before 

 the end of June. This unhealthy condition of the tree 

 without an apparent cause is known as carpoptosis, and 

 is ascribed to a weak or defective fertilization, as it 

 occurs more frequently when the blooming season had 

 coincided with a long spell of wet weather, which washes 

 off the pollen and interferes with the beneficial action of 

 bees and other pronubal insects. It has been long 

 known to our gardeners that orange groves in which 

 bee-hives are kept are always more productive than 

 those in which there are no bee- hives, or which are 

 not much visited by bees, and therefore our gardeners 

 are glad to see the bees busily humming on the orange 

 trees in bloom. It is not easy to establish accurately by 

 experiment what is the actual increase of production due 

 to fertilization by bees, but it is generally believed to be 

 15 to 20 per cent, and may be much more in certain 

 circumstances. The honey obtained from the orange 

 grove, though fine in quality and very light in colour, is 

 lacking in flavour, and on this account it is often allowed 

 to remain in the hive to be used by the bees, in order 

 not to have to feed them artificially for a considerable 

 part of the year, 



4. DISEASES CAUSED BY PARASITIC FUNGI. Citrus 

 trees are subject to a legion of fungous parasites 

 which have been so ably described and most of them 

 figured in Otto Penzig's work 4< Stndi Botanici sugli 

 Agrumi". But on account of their comparatively innocent 

 character, or of their mild attacks, many of them never 

 attracted the attention of cultivators, and are economi- 

 cally unimportant. A knowledge of the following diseases 

 will be found sufficient by the practical grower. 



Gummosis or gumming ^ the mat della gomma of 

 the Italians is an infective disease due to the presence of 



