2 INSECTS AFFECTING THE ORANGE. 



dies back, and finally the older portions of the tree become affected and 

 gradually succumb. 



A morbid growth undoubtedly of fungus origin invariably accompa- 

 nies the disease in its advanced stages. This appears first as discolored 

 patches or slight swellings, which gradually become confluent, and fin- 

 ally burst, forming an eruption of brownish color. The older branches 

 become covered with ridges of exfoliated bark and exudations of gum, 

 Ijresenting an unsightly appearance, not unlike that of "Black-knot" on 

 the plum. 



The peculiar microscopic fungus which causes "die-back" is undoubt- 

 edly well known to mycologists. The disease yields readily to treat- 

 ment with dilute carbolic or creosote washes, and is curable by these 

 simple means, provided the exciting cause is removed. This fact may 

 be regarded as confirmatory of its fungus character. The term "die- 

 back" has been applied to several other diseases of the orange, and 

 even to injuries from frost, but the affection above described is the one 

 "which is generally known under this name. 



The exciting cause of "die-back" has been variously ascribed to over- 

 fertilization, deep planting, imperfect drainage, the presence of humic 

 acid in the soil, and finally to insects. While there is good reason 

 to suppose that conditions of the soil, or of cultivation unfavorable to 

 the growth of the plant, render it liable to the attacks of fungus dis- 

 eases, there is no evidence that in this case its presence is due to the 

 depredations of insects. It is true that the dead and dying branches of 

 trees affected with die-back attract boring insects of various sorts, but 

 these are found to belong to wood-eating kinds, which act as scaven- 

 gers merely, and have no connection with the disease itself. 



Bark-fungus.— (Plate II, Fig. 2.) Many forms of lichens attach 

 themselves to the trunk of the Orange, in common with other trees, and 

 flourish abundantly in dark and damp situations. There are, however, 

 several mold like fungi found more exclusively upon the Orange and 

 its allies. These bear a deceptive resemblance to incrustations of Scale- 

 insect. 



Of these fungi the one most readily mistaken for Scale-msects com- 

 monly appears upon the trunk and branches as little hard excrescences 

 of gray color, which, in wet weather, burst, disclosing a white cottony 

 interior, from which they are often confounded with the " Mealy Bug," 

 {Dactylopius). The resemblance to the Coccid is increased when the 

 white spicules, a bundle of which fills each little fungus cup, are beaten 

 out by rains, and felted upon the bark in a mold like coating. The 

 fungus is confined to the surface of the bark, and appears to germi- 

 nate exclusively among the debris of Scale-insects. It is always found 

 upon trunks that have long been coated with Chaff Scale {Parlatoria 

 pergandii). It may also be found upon the leaves when they have be- 

 come infested with this scale, and is easily removed by gentle friction 



