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. No breeding act has been seen to 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 efifect 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. — Plum-pocket fungus and loose-weft fungus. 1. A loose wefted collection of 

 spore sacs, which is surrounded by barbed threads. A loose-weft fungus. 2. A small 

 group of threads from 1, bearing a number of sacs. 3. Same as 2, showing a single 

 sac with its sac-spores. 4. Plum-pocket fungus. Shows the spore-sacs of a plum- 

 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 sacs. All highly magnified. 

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



poplars and cottonwoods and sumacs are also attacked by 

 them. (Figs. 49, 193.) 



Loose-weft fungi (Gymnoascacecs). Very closely related to 

 the slime-flux 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. Many are found exclusively on feathers, 



