ENTOMOLOGY. 415 



This disease is only too well known in its effects, as it sometimes 

 causes an almost total loss of the peach, plum and cherry crops. At 

 present it is not a common disease in Minnesota, though by no 

 means an unknown one, as I have observed it upon wild plums, 

 cherries and shad-berries in Otter Tail county and elsewhere. The 

 disease is called brown rot, because the fruit becomes brown 

 skrunken and shrivelled, so that nothing- remains but a tough skin 

 enclosing the stone; and this sorry looking object, resisting further 

 decay, remains for a long time hanging to the tree (Fig. 4, e). If we 

 investigate the fruit before it becomes "mummied", or "mummy- 

 fied," or before it turns brown, we can see its surface densely cov- 

 ered with tufts of ash-colored spores. The vegetative threads of the 

 fungus extend through the tissues of the fruit, force their way to 

 the surface, and produce spores arranged in chains (Fig. 4, c). As 

 the disease is bj^ no tneans a stranger in the orchards of the Experi- 

 ment Station I have frequently used the microscope to study mum- 

 my-plums collected for the purpose from the trees or from the 

 ground under them. Although apparently devoid of life and harm- 

 less, such fruits are most dangerous to the orchard. If we place one 

 of them in moist surroundings we will perceive in a very few days 

 that it is thickly covered with tufts bearing spores (Fig. 4, a, b), and 

 these do not belong to fungi growing simply upon decaying fruit. 

 A microscopic study of the dry flesh of such a plum reveals numer- 

 ous threads, which are composed of large and thin-walled cells, and 

 it reveals also single cells with thick walls of irregular shape. These 

 latter are evidently resting vegetative cells or gemmae. They are 

 well adapted to withstand the rigors of winter and will gerininate 

 as soon as conditions are favorable. Other investigations made in 

 the house showed plainly that the spores appearing as chains upon 

 the surface of the fruit during summer also germinated readily and 

 produced spores again. These latter, as soon as they become de- 

 tached, germinate again, and there is no doubt that their germ- 

 threads can enter the skin of a fruit that is not injured, though as a 

 rule there are insects enough to make openings for their entrance. 

 .When such threads enter the tissues of flowers, leaves and tender 

 twigs they spread rapidly and kill them (Fig. 4,*c?). Later the 

 threads force to the surface and multiply again. The fungus can 

 be detected on the flowers at about the time that their petals drop. 

 At first a slight discoloration appears and this rapidly increases 

 until the flower becomes brown. Such dead flowers remain fre- 

 quently upon a tree for many weeks, or until washed down by heavy 

 rains. Whenever such rotten and sticky flowers come in contact 

 with leaves, etc., they communicate the disease, and as a result the 

 parts affected decay also. Upon leaves the fungus shows first as a 

 slight discoloration which spreads gradually until the larger part 

 of a leaf is involved and turns reddish-brown (Fig. 4, d). Both sides 

 of the leaf are affected, though the upper surface seems more apt to 

 be injured. During wet weather the infested leaves show numerous 

 tufts of fungi, and they have a powdery or mealy appearance caused 

 by the innumerable spores. During this period the parts affected 

 are highly infectious. 



