140 Minnesota Plant Diseases. 



plants are very minute and can usually only be clearly seen un- 

 der a compound microscope. On the one hand these fungi 

 show relationships with the sphere fungi, which are undoubted- 

 ly their closest fungus relatives. They form sacs containing 

 spores and these are contained in sac-capsules. The structure 

 of the sac-capsule is not however very similar to those of the 

 sphere fungi. The cases are often long pear-shaped and the 

 sacs are produced over a considerable period of time and do not 

 all mature at once. Moreover, the sac-cases are preceded by a 

 breeding act which is altogether unlike that of any of the sphere 

 fungi but can be best compared with the breeding act in the 



FIG. 61. A common cup fungus (Urnula craterium) growing on sticks sunken in the soil 

 and appearing abundantly in the spring. Original. 



group of algae known as the red sea-weeds. The structure of 

 the mycelial threads is, moreover, very similar to that of the 

 red sea-weeds and the beetle fungi are therefore considered by 

 some botanists to have a common origin with that group of 

 algae. The beetle fungus plants are usually broom-brush- 

 shaped and are found on the legs and wings and outer parts of 

 insects. They are often highly specialized in locality, occurring 

 only on certain joints of the legs and on certain legs of the 

 host. The plants are often of two sexes though some contain 

 both female and male organs. These fungi are undoubtedly 

 numerous in Minnesota though no attempts have as yet been 

 made to collect or determine them. They seldom, however, 

 are very destructive parasites, as is the caterpillar fungus or the 



