10 A Monograph of the Erysiphaceae 



a stream of very small, biguttulate spores, 6.5-10.5 x 3.5-6^« 

 in size, immersed in a colorless mucilaginous substance. In such 

 cases there may usually be found on the same mycelium paler and 

 smaller bodies, globular, oval, orpyriform in shape, without appen- 

 dages, and containing the same kind of spores. Similar bodies 

 are frequently formed in the joints of the conidiophorcs when they 

 usually bear at their apex the shrivelled remains of the chain of 

 conidia. 



Prior to De Bary's searching investigations into this subject in 

 1870 (99), these bodies were known as pycnidia, and the con- 

 tained spores as st}'lospores, and by the older botanists were thought 

 to be another form of reproduction of the Erysiphaceae. De Bary, 

 however, showed that the pycnidia and spores belonged to a minute 

 fungus living parasitically within the hyphae of species of the Ery- 

 Iphaceae. The vegetative mycelium of this parasitic fungus {Am- 



peloniy 



closely 



septate hyphae, which run singly inside the hyphae of the host. 

 The fruit of the Ampclomyces is produced either in the pcrithecia, 

 conidiophorcs, or cells of the host mycelium. If the species 

 attacked is in the perithecial stage, the parasite forms its fruit in 

 the interior of the perithecium, absorbing the asci and sometimes 

 sending its hyphae into the appendages. The variation in shape 

 of the pycnidia is due to the difference in the maturity of the peri- 

 thecia attacked. If the host is in the conidial condition, the fruit 

 of the Ampelomyccs is produced in the transformed cells of the 

 conidiophorcs, and in this case the presence of the parasite seems 

 to prevent any subsequent formation of perithecia. 



De Bary succeeded in infecting germinating conidia of species 

 of the Erysiphaceae with the spores of Ampelomyces, and found 

 that the latter on germination at once penetrated the germinal 

 hyphae of the conidia. In some cases, the spores of the Ampclo- 

 myces germinated after they had been kept for three months in a 

 dried condition. They are, therefore, probably capable of infect- 

 ing fresh hosts after passing through the winter in a resting state. 

 Ampclomyces has been observed on most of the species of the 

 Erysiphaceae, and no doubt plays an important part in checking 

 their spread, by lessening their vitality, and often preventing the 

 formation of perithecia (see Griffiths, 153, pp. 18*4, 185). 



