Fungous diseases of plants . hefungus is more generallyknown in America. Itis a brown rot, begin-ning as a small spot, fre-quently near the bud endof the fruit, and spread-ing until the whole fruitmay be involved. Thereis not such characteristicshrinkage of the tissuesas in the case of the bit-ter rot. The pycnidialpustules may begin toappear when the spot isonly half an inch in di-ameter, or they may notbecome evident until theentire fruit is rot often attacksthe fruit on the trees,yet it is far more com-mon upon the neglectedfallen fruit (Fig, 169),which is a great sourceof dang
Fungous diseases of plants . hefungus is more generallyknown in America. Itis a brown rot, begin-ning as a small spot, fre-quently near the bud endof the fruit, and spread-ing until the whole fruitmay be involved. Thereis not such characteristicshrinkage of the tissuesas in the case of the bit-ter rot. The pycnidialpustules may begin toappear when the spot isonly half an inch in di-ameter, or they may notbecome evident until theentire fruit is rot often attacksthe fruit on the trees,yet it is far more com-mon upon the neglectedfallen fruit (Fig, 169),which is a great sourceof danger to the healthof the tree. In the mild-est form the canker is believed to cause merely a greater rough-ening of the bark, an injury which may occur as a single spot,or which may extend along the limb for a distance of several the most serious cases it first destroys the bark, well-markeddepressed areas being developed, about which local swellings ofthe limbs occur, and in these affected areas the wood at the center. Fig. 170. The Sph.^ropsis Canker of Apple(Photograph by H. H. Whetzel) 352 FUNGOUS DISEASES OF PLANTS may be exposed, or extensive wounds may result. The disease ismore common upon the larger limbs of older trees, but trunks andtwigs are not exempt, and young trees may suffer. When completegirdling results, the limb is killed, yet serious consequences maygradually develop without girdling. Fig. 170 shows an early stageof this canker. Infection is probably most frequent in the spring. It is believedupon good evidence that the worst wounds occur only when thefungus gains entrance to the edge of the wood through which sunscald badly on the parts exposed to the directrays of the southwest sun are as a rule subsequently infested withcanker. In New York the Spitzenburg and Twenty Ounce arementioned as the most susceptible varieties of apple to the limbcanker, while Baldwin, Wagoner, Greening, and King follow inthe order given ; the Tallman Sweet was
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