54 ANNUAL REPORT. 



shell, filled with powder, ready to fall before a puff of wind that would 

 once scarcely have stirred its larger branches. This is the result of 

 the slow but sure growth of a fungus which ordinaril}' lives and car- 

 ries on its destructive work within the tree for years before it can be 

 seen by the naked eye. How it lives may be shown by comparison 

 with the well known process of cultivating mushrooms, in which, 

 after a suitable bed of compost is prepared, bits of spawn are set as 

 "seed." To the eye this spawn is nothing but turf or manure, trav- 

 ersed by a few mouldy threads; but from it the threads, which are the 

 feeding organs (mycelium) of the mushroom, spread into every part of 

 the bed, working over the crude, dead manure, until it is transformed 

 into a part of their own substance, when the}'' suddenly develop the 

 growth that we prize for our tables, iii'o, when a branch is cut from 

 an apple tree, and the wound fails to heal over, a spore or reproduct- 

 ive cell, exceedingly minute, falls upon the wound and develops a 

 mycelium in the healthy wood, on which it feeds until it has effected 

 its work of destruction. Sometimes years pass before it shows itself 

 in any form other than this microscopic growth; but ultimately, in 

 some sorts of canker, it fruits in a form visible to the naked eye. 



•-•^'' '"'^ Another common fungus of the apple, 



but one very unlike the toadstools, is 

 that (Fusicladi2im dendriticum,) which 

 has attracted much attention of late 

 years as the scab and leaf-mildew. To 

 sustain its own life it needs the nutri- 

 tious substances elaborated by the leaves, 

 Scabs on Apple. Natural size. ^Or does it hesitate to freely take them; 



leaving the twigs weakened, to make a spindling, sickly growth, if 

 they succeed in growing at all, as the season goes on, and with so lit- 

 tle vitality that a severe winter, like the last, is fatal to them. The 

 gnarled, cracked and blackened Snow-Apples that, alone, can be rais- 

 ed in many localities, testify with equal force to the destructive power 

 of the same parasite when it seats itself upon the young fruit.* 



Many orchards aro affected by a white mildew that appears on the 

 young leaves or, more especially, on the twigs. When in its most 

 vigorous summer growth, like the mildew of the rose or the verbena, it 

 well deserves this epithet, which, however, is less expressive than the 

 German word that it corresponds to. Mehlthau — meal-dew aptly ex- 

 presses the mealy appearance of the diseased parts, which are covered 



*Thi8 fnngiis is discusped at some length in the Report of the Wisconsin Experiment Station, for 

 1883, from wliich the accompanying figures are copied. 



