Minnesota Plant Diseases. 171 



celium stimulates the leaves or stem to excessive growth, and 

 gall-like swellings, often reddish in color, are thus produced. 

 On the surfaces of these galls the palisades of basidia are pro- 

 duced, and the basidium-spores appear to the naked eye as a 

 fine white powder. Four spores are produced on each basid- 

 ium. These spores germinate by forming a thread, which is 

 again capable of causing infection. The galls so produced are 

 fungus-galls and must be distinguished from- the insect galls of 

 plants which are much more common in occurrence. The 

 most common Minnesota member of this group is one which 

 forms galls on Labrador tea in the northern part of the state. 

 The gall on blueberry and cranberry undoubtedly also occurs 

 but it is not very abundant and good specimens have not been 

 collected. (Figs. 37, 81.) 



Mold palisade fungi (Hypochnacece). These comprise the 

 simplest of all palisade fungi since no true fruiting body is 

 formed but merely a dense mold-like mass on rotting logs or 

 decaying wood. On the surface of this mold-like mass are the 

 basidia arranged irregularly and only suggesting the true pal- 

 isade of the higher groups of this alliance. 



Smooth shelf fungi (Thelcphoracece). In this group of fungi 

 the palisade is usually the under surface of a shelf-like fruiting 

 body. In some forms, however, the fruiting body is prostrate 

 and closely grown to the log or substratum on which it grows 

 and no part of it shelves out. In this case the whole upper sur- 

 face is covered with a palisade. Such prostrate forms often ap- 

 pear as thin, grey-brown or whitish crusts on the bark of dead 

 twigs and trunks of trees. Whatever the form of the fruiting 

 body the palisade surface is always smooth and in this respect it 

 differs from the pore and gill fungi. The palisade surface, 

 moreover, is not entirely composed of basidia but may contain 

 certain sterile cells of peculiar structure, known as cystidia. 

 They are usually long, sharply-pointed cells which project 

 from the surface very considerably and are frequently coat- 

 ed with certain salts which give to them additional rigidity. 

 Their function is probably protection. When occurring in 

 great numbers they give to the palisade surface a velvety ap- 

 pearance as seen by the naked eye or under a low-power hand 

 lens. The smooth shelves are very common Minnesota fungi 



