Minnesota Plant Diseases. 139 



are not in all cases dangerous diseases. Moreover, not all of 

 the sphere fungi are parasites ; many are saprophytes as are the 

 dung fungi, and many are half saprophytes or wound parasites. 

 (Figs. 35, 60, 153, 183 to 187.) 



Dead-stick and burnt-wood fungi. These are sphere fungi 

 which are found in great abundance on dead sticks and branches 

 of trees. They are saprophytes or half-saprophytes and the 

 latter do not usually produce their sac-capsules until after the 

 death of the host branch. The sac capsules are very often col- 

 lected together with or without a black myceUal cushion, and 

 they usually break out from beneath the bark, pushing out the 

 latter before them. Often the mycelial cushion is of great size 

 and thus resembles the black-knot in appearance. Such fungi 

 occur in great abundance on oak limbs or oak fence posts and 

 sometimes produce cushions a foot in length. These cushions 

 become black and hard and resemble burnt or charred wood, 

 whence their common name. They are often mistaken for 

 such wood by those unacquainted with their true nature. 

 Birch branches and in fact limbs and stumps, dead or fallen 

 trunks of almost any tree may show such burnt wood fungi. 

 They are very effective agents of decay in wood, though not as 

 conspicuous in their action as the pore and gill fungi of the 

 mushroom group. The highest forms of these burnt wood 

 fungi produce cushions which are club-shaped in appearance 

 and look like charred club fungi. A number of such forms are 

 abundant in our state. In the spring one finds such clubs cov- 

 ered with a white dust of accessory spores, while in the iall the 

 sac-cases are formed and the club is black and warted just as in 

 black-knot. 



In some of these dead-stick and burnt-wood fungi one finds 

 sac-capsules which open, not by a pore, but by long slits or by 

 star-shaped openings. It is in these forms that we see the 

 transition to the cup fungi ; for a cup of the cup-fungus group 

 is merely a sac-capsule with a great wide-open top. It has a 

 pore which has become very large so that the capsule when ma- 

 ture has a beaker shape, or may even become saucer-shaped or 

 plate-like in form. 



Beetle fungi (Laboulbeniinecs). These fungi are parasites on 

 insects and are found in abundance on water beetles. The 



