Minnesota Plant Diseases. 



121 



leaf or pocket, and at right-angles to its surface. They arise 

 just under the cuticle which is pushed up and sloughed off as 

 the spore-sacs ripen. Xo breeding act has been seen tp pre- 

 cede the spore-sac formation. The sac-spores are often capa- 

 ble of budding in yeast fashion when placed in sugar solutions, 

 and in some of the fungi they bud in this fashion before they 

 are released from the sac so that the latter may then contain 

 a large number of spores. In addition to the effect upon fruit 

 and foliage of plums, these fungi often cause witches'-brooms 

 on cherries and plums as well as on birches and alders. Oaks, 



FIG. 49. 1'lum-pocket fungus ami loose-weft IHIIKH- 1. A loose wcfted collection of 

 spore sacs, which is surrounded by barbed threads. A !<.- wi it fungus. 1*. A smill 

 group of threads from 1, bearing a number f MCS. It. Same at -'. showing a single 

 sac with its sac-spores. 4. Plum pocket fungus. Shows the *|>ore-sacs of a |>lum 

 pocket fungus arranged in a palisade on the surface of the pocketed plum; c the cells 

 of the plum; m fungus threads and h the fungus spore sics. All highly mtgniried. 

 1, 2, 3 after Sachs; 4 after Hillary. 



poplars and cottomvoods and sumacs are also attacked by 

 them. (Figs. 49. 193.) 



Loose-weft fungi (Gyntnoascaccff) Very closely related to 

 the slime-tlux fungi are the loose-weft fungi. The spore sacs 

 are borne in dense clusters on a very loose weft of threads and 

 in no regular arrangement. In some, there is a loose system 

 of threads surrounding the cluster, forming a covering not un- 

 like a large-holed basket. These* threads are also usually 

 armed with tiny spines. Such a covering is merely an ama- 

 teurish, spore-sac capsule. The loose-weft fungi are peculiar 

 in their habits. Manv are found exclusively on feathers. 



