Minnesota Plant Life. 



85 



Twig-fungi. A large group of black fungi grow upon twigs 

 and these may be known generally as twig-fungi. One of the 

 most prominent forms is the black knot of plum and cherry 

 twigs, a plant which is very common upon various species of 

 wild plums in Minnesota, and upon the wild choke-cherry. 

 It forms black swollen bodies, half an inch or so in height, 

 and two or three inches or more 

 in length, distorting the twig 

 where it grows, and bursting the 

 bark to display its layers of black 

 fruit-bodies. A close examina- 

 tion of a black knot mass will 

 show that its surface is covered 

 with little round emergences or 

 pustules, and each emergence 

 marks the point where a bottle- 

 shaped fruit-body is imbedded in 

 the general layer. As before no- 

 ticed, each fruit-body contains its 

 lining of sacs in which the black 

 knot spores are found — for the 

 elaboration of which the plant- 

 body derives sufficient s u s t e- 

 nance from the cells of the twig 

 which it robs of its sap. The 

 black knot is but a single exam- 

 ple of a large group of black 

 twig-fungi. Some of them like 



the black coin-fungus form coin- 



FiG. 31. Fungus spot-disease on leaf of 

 false vSoIunion's seal. After Hal- 

 sted. 



shaped discs. Others develop a 

 few little gourd-shaped fruit- 

 bodies in a group. One curious kind of which there are in 

 different parts of the world about 400 species known, forms on 

 twigs little black patches in which three or four fruit-bodies are 

 imbedded, one of the group being entirely different from the 

 rest. The central one, in its bottle-shaped cavity, produces 

 spores displayed on stalks, while the others produce spores de- 

 veloped in sacs. The spores produced on stalks are much 



