78 Minnesota Plant Life. 



surface of the cup, but rather the sacs themselves with the spores 

 enclosed. 



A particular variety of cup-fungus, very abundant in the 

 woods of Minnesota, grows upon the ground and produces a 

 hard, black underground tuber, as large as the end of one's 

 thumb. This tuber has a firm skin, but when it is cut open the 

 interior is softer and white. A bud forming under the skin of such 

 a tuber develops a fruit-body, cup-like in shape, and provided 

 with a slender stalk. A relative of this fungus produces on the 

 twigs of tamaracks nut-like swellings from which little cups 

 arise. 



Maple-leaf tar spots. A great variety of cup-fungi and disc- 

 fungi are parasitic upon the leaves of growing plants. Possibly 

 the most conspicuous one in Minnesota is the tar-spot fungus 

 of the maple, often seen developed on the upper surfaces of 

 maple leaves as one or more black shiny bodies, a quarter of 

 an inch or so in diameter, and of an irregular roundish shape. 

 These are the fruit-bodies of the tar-spot fungus, and while the 

 vegetative portion of the fungus is growing within the tissues 

 of the leaf, the reproductive portion, consisting of a layer of 

 sacs with spores enclosed, destroys the epidermis of the leaf and 

 produces the conspicuous spot. 



Truffles. The fruit-bodies of a few sac-fungi are developed 

 underground and here belong the truffles, which may be de- 

 scribed in a general way as underground cup-fungi, in which 

 the cups have closed up into irregular egg-shaped bodies. Upon 

 the rotting of the truffle the labyrinthine sac-layers are exposed 

 and the spores escape. Truffles are among the most esteemed 

 delicacies of the gourmet. 



Green and blue moulds. Curiously enough the green and 

 blue moulds which occur on bread, leather, decaying fruits and 

 other objects of that sort are rather close relatives of the truffles. 

 As was observed during the description of the rust-fungi, a 

 fungus often has the power of producing more than one kind 

 of fruit-body. The blue mould if for a sufficient time left to 

 itself will form in addition to the ordinary patches of blue 

 spores arranged in chains on swollen terminal cells of some of 

 its threads, also certain miniature yellow truffles, not much 

 larger than a pin-point. These little truffle-like fruits, just as 



