1 64 DISEASES OF CULTIVATED PLANTS 



Pcnzigii (Sacc.) and M. camelliae (Sacc.), but probably other 

 species, or even members of other genera, form similar sooty 

 films on the leaves and fruit of living plants in different 

 countries. M'Alpine has shown that the sooty patches 

 occurring on fruit and leaves in Australia are distinct species. 

 On the leaves and fruit of the orange, citrus, and lemon, these 

 fungi form a compact black membrane, which frequently 

 cracks and peels off in flakes during dry weather, leaving the 

 surface upon which it rested quite clean and apparently 

 uninjured, although at the same time much injury is caused 

 by preventing leaves from performing their functions, whereas 

 when the fruit is more or less covered by the fungus it is 

 rendered unsaleable. These fungi are not parasites in the 

 sense of obtaining food from the host through mycelium 

 permeating the living tissues, but assimilate 'honey-dew' 

 deposited on the leaves by aphides or species of green-fly, 

 etc., consequently if trees are kept free from these insect 

 pests, sooty mould would not be present. 



M. Penzigii. Mycelium forming a black crust which readily 

 peels off; perithecia seated on the mycelium, subglobose, 

 black, 150-160 p diam. Asci pear-shaped, 8-spored; spores 

 ovate-oblong, 3-septate, with one or more vertical septa, 

 hyaline then tinged brown, 11-12 X4~5 /A. Several secondary 

 or conidial forms of fruit have been described. 



M. camelliae. On leaves of camellias. 



Swingle and Webber, who have paid much attention to the 

 subject, have come to the conclusion that ' resin- wash ' is the 

 most effective remedy for destroying the various kinds of 

 insects that secrete 'honey-dew.' Spraying should be done 

 when the insect is in the larval or pupal condition, and as 

 this period differs in time in different countries, careful 

 observation should be kept. 



Fumigation with hydrocyanic gas has also proved effective, 

 and trees should be exposed to the fumes for about forty-five 

 minutes, and should be done when the temperature is low. 

 It has also been pointed out by Webber that the species of 

 fungi belonging to a genus called Aschersonia are parasitic on 

 the insects producing honey-dew, and are often present in 

 large numbers, and he considers that these fungi might be 

 introduced and fostered, as a means of keeping the insects in 

 check. Many attempts have been undertaken to utilise 

 parasitic fungi as a check to the ravages of various insects, 

 but unfortunately without much success so far; nevertheless 



