64 Minnesota Plant Diseases. 



to the stem upon some wound, which will remove the protect- 

 ing cork layer from the wood. Many burnt wood fungi in- 

 habit stems both herbaceous and woody. On the latter are 

 very often found the gill fungi or mushroom allies and the 

 pore fungi. These fungi are in general long-lived, living from 

 year to year on a tree trunk and storing up nourishment in 

 their mycelia. Months and even years of preliminary growth 

 are often required of such fungi before the spore-bearing or- 

 gans are produced. Enormous numbers of spores are then 

 formed and a new crop may be shed every year until the nour- 

 ishment in the tree trunk is exhausted. 



Root- inhabiting parasites. The root is not as popular a 

 resort for parasitic fungi as either the leaf or the stem, but not 

 a few find a congenial abode in these parts. They have similar 

 difficulties to meet as the stem dwellers and are in fact mostly 

 members of the same groups of fungi. Often the same fungus 

 is capable of growing up into the tree trunk. The spore-bear- 

 ing organs are always found either at the surface of the ground 

 or in air-spaces in the soil, such as in the burrows of rabbits. 

 In certain grass-like plants a smut is found in the roots and 

 causes the formation of swollen pear-shaped bodies. 



Fruit-inhabiting parasites. A very large group of fungi 

 inhabit the fruits of flowering plants. The fruits, whether 

 they be fleshy, like apples, or hard, like nuts, have always some 

 protective coat, which is a serious obstacle against an invading 

 fungus. Some fruits are better protected than others in this 

 respect and the weaker may prove vulnerable to fungus attacks, 

 e. g., when thin-skinned apples are invaded by mold rots. The 

 smuts, which are commonly found in the grains of grass- 

 plants, have devised an ingenious method for a successful at- 

 tack upon the fruit of the grasses. The fungus gains entrance 

 to the stem of the plant when the latter is in the seedling stage 

 and then keeps pace with the growing plant without appar- 

 ently affecting it at all detrimentally, until the grains are com- 

 mencing to fill. Then the fungus permeates all of the grain 

 tissues, appropriates the food material and forms its smut 

 spores. The ergot .of rye and other grains has still another 

 device for attacking the grass fruit. It does not, as the smut, 

 live in the point of the stem until the fruit is formed, but at- 



