An Orchard Scourge. 203 



so scarred and spotted as to be practically worthless, except for stock or 

 cider. Pears, after having gained considerable size, were seen to have been 

 affected over great areas of their surface by the injuries received, while still 

 ■quite young, the later appearance being a rough, discolored surface, though 

 " scabs " similar to those on the apple were plentiful enough. In the case of 

 both fruits, the unyielding coating of destroyed tissues gave way to the in- 

 ternal forces of expansion, and cracks, more or less deep, occurred. In 

 Champaign county the Early Harvest apples, among others, were divided 

 half way to the core, or even deeper, by several irregular fissures, leaving 

 knobby lobes, more or less covered by a layer of blackened, corky tissues. 



It is well known that " scabby "" fruit, besides being injured in appearance, 

 much sooner decays, at least in a great majority of instances. Rot begins at 

 the " scab," and proceeds inward and around. Often this occurs while the 

 fruit still hangs on the tree, and almost certainly takes place if scabby ap- 

 ples or pears are gathered and stored in a moist place. 



Appealing to the microscope, we find all these injured parts of the trees and 

 fruit bear the vegetative threads (mycelium) and spores of a fungus, specific- 

 iilly the same whether on the leaves, the twigs, or the surface of the fruit. 

 However different the appearance to the unaided eye the injury may be on 

 these different parts, there is no appreciable difference in the microscopical 

 •characteristics either of the fungus or in the real destruction of the cells and 

 tissues. However different the appearance to the unaided eye the diseased 

 spots or patches were, occurring on the leaves, twigs or fruit, anyone com- 

 petent to judge in such matters would, upon microscoi^ical examination, 

 pronounce the fungus specifically the same in all cases. Its mode of growth 

 and development is essentially the same on all parts of the tree, save svich 

 modifications as, evidently enough, arise from the difference in the parts 

 themselves. On the fruit, the epidermis and perhaps a few layers of cells are 

 destroyed, while the deeper tissues continue to live and grow. On the leaves, 

 the epidermis is similarly destroyed, but, on account of the thinness of the 

 leaf, the whole structure goes with it. The scars on the twigs somewhat 

 resemble those on the fruit, but instead of being circular, or nearly so, they 

 are elongated in the direction of the fibers; usually, also, they are much 

 smaller. 



By proper manipulations it is easy to make out that the mycelium of the 

 fungus consists of a few colorless, frequently branched, incon.spicuous threads, 

 woven loosely through and through the cells of the supporting plant. This 

 poorly developed mycelium neither wanders far nor penetrates deejily. On 

 the fruit, it is confined to the spot which eventually shows the characteristics 

 of the disease, and to the surface layers of cells. From the white threads 

 there arise short, erect, tinted portions, Avhich, from their density, form a 

 velvet-like mat covering the aftected spot. On the outer ends of these mi- 

 nute stalks the multitude of spores is borne, and these being dark olive- 

 brown, or in the mass almost black, give to the spot the color observed. The 

 spores are usually about four times as long as wide, often .somewhat club- 



