74 MYCOLOGY 



the fruit is enlarged by the attack of the fungus at the expense of the 

 stone which fails to develop. The hollow galls on the plum are due to 

 Exoascus pruni. The so-called cedar apples on our red cedar trees in 

 the spring are caused by the attack of an annual rust fungus, Gym- 

 nosporangium juniper i-virgini ana, and from the surface of these 

 apples two-celled spores arise. The white rust of cruciferous plants, 

 Cystopus candidus, produces blisters on the leaves and stems of shep- 

 herd's purse. The black knot of the plum is a tumor-like swelling of 

 the branches of plum trees due to the attack of an ascomycetous fungus, 

 Plowrightia morbosa (Fig. 22). Large swellings on oak trees the size of 

 a man's head and over are caused by a fungus, Diachana strumosa, and 

 some of these swellings may be the size of a large pumpkin. Galls due 

 to insects are frequent on plants, but a discussion of them is extralimital. 



According to conditions of environment, we may briefly treat of 

 fungi as hygrophytic, mesophytic and xerophytic forms. The hygro- 

 phytic forms include the aquatic fungi, such as Achlya^ Mono- 

 ble pilaris, Saprolegnia and other genera which live and carry on 

 their reproduction in water. Perhaps to this group would belong 

 a fungus of the genus Cyttaria, which was found by Darwin in the 

 beech (Nothofagus) forests of southern Patagonia. The beech trees 

 grow in cold, wet valleys completely barricaded by great moulder- 

 ing trunks of former beech trees on which the globular, bright yellow 

 fructification occurs and which is eaten by the Fuegians. 



The mesophytic forms include many of the common fleshy gill 

 fungi that live in our woods and forests, appearing in surprisingly great 

 numbers after a spell of wet weather. Here we might include species 

 of Amanita, Boletus, Russula, and Clavaria and others which are not 

 infrequent, while in our meadows occur mushroom and coprini. Three 

 conditions seem favorable to their growth: abundant leaf mould, 

 warmth and abundant moisture. 



The habitats of the fleshy fungi are of general interest. Collybia 

 platyphylla develops its fruit bodies on the shaded side of decaying 

 logs. The fairy-ring fungus, Marasmius oreades (Fig. 23) produces its 

 sporophores in lawns in the form of rings long known as fairy rings. 

 Frequently grassy spots are enclosed by the circle of toadstools which 

 are several feet in diameter. The fruit bodies of Pholiota adiposa 

 (Fig. 24) grow from wounds in living trees. 



In forest operations the slash, when scattered, rots more rapidly 

 than when piled. This is due to the fact that two types of fungi 



