OTHER SAC FUNGI 



253 



The caterpillar and grub fungi. These extraordinary parasites 

 (Cordyceps) grow in the bodies of certain caterpillars and other 

 larvae, and in their pupae. The body cavity of 

 the insect becomes filled with the mycelium, 

 and generally mummified, after which a long- 

 stalked sac fruit grows out from between cer- 

 tain segments (Fig. 225). 



The truffles. The truffles are very remark- 

 able sac fruits, sometimes as large as pota- 

 toes, developed underground on my- 

 celium that is generally associated 

 with the roots of certain trees. The 

 commonest truffle on the market 

 (Tuber brumale) comes from the re- 

 gion of Perigord, in central France, 

 and is the most prized of all the edi- 

 ble fungi. It grows under certain 

 kinds of oak trees, and is found by 

 dogs and swine that are trained to 

 discover its location, and which detect 

 the fungus by a characteristic odor. 

 The association of the mycelium of 

 the truffle with the roots of 



the oak tree is an excellent 

 ^ le of what ig called 



a mycorrhiza, and is dis- 

 cussed in Sec. 278. 



The spot fungi and rots. 



FIG. 225 



FIG. 224. The ergot 

 (Claviceps) 



A, ergot grains on a 

 head of barley; B, 

 small sac fruits (as- 

 cocarps) developing 

 from an ergot grain. The spot diseases of plants Caterpillar fungus 

 B after Tulasne i n (Cordyceps) errow- 



a> ai are numerous, and mostly 



J ing out ot the 



upon the leaves and fruit. Many of them are larva of the May 

 caused by sac fungi, as the strawberry-leaf spot beetle, which lives 

 (Sphcerella), black spots on grasses and clover un er & roun 

 (Phyllachora) resembling rust spots, tar spots on willow and 

 maple (Ehytisma), and the apple scab (Venturia). Some of the 



