2 Raymond J. Pool 



in great abundance on simple, erect sporophores, the small glo- 

 bose indehiscent perithecia (cleistocarps) provided with appen- 

 dages of definite form, containing asci with large, non-septa.te 

 spores. 



Structure and Round of Life 



The mycelium consists of many delicate, silky, white or color- 

 less or sometimes brownish filaments or hyphae with many cross 

 partitions at rather long intervals. The hyphae are often 

 branched and interwoven so that a more or less densely tangled 

 and felt-like mycelium is produced in many species. In all the 

 genera except Phyllactinia, hyphae of the vegetative mycelium 

 produce off-shoots at intervals which pierce the outer walls of 

 the host cells and swell into bladder-like structures (Plate II, 

 figs. 16-17), haustoria, in the epidermal cells. The function of 

 these haustoria is double, to attach the fungus to the host and 

 to serve as absorbing organs which draw nutrient material from 

 the epidermal cells and pass it out to the external mycelium upon 

 which the conidia and perithecia are formed. However, in the 

 genus Phyllactinia we have an interesting and important differ- 

 ence in the matter of the formation of the haustoria. In this 

 genus haustoria are not sent into the epidermal cells of the host, 

 but instead special hyphal branches, of limited growth, are de- 

 veloped which enter the host tissue by way of the stomata. 

 Once inside, these branches wind about in the inter-cellular air 

 spaces and finally send haustoria into the surrounding cells. 

 These special hyphae consist usually of more than one cell (up 

 to three or rarely more), but in all cases the haustorium is pro- 

 duced by the last cell of the filament. The haustorium itself 

 is similar to the haustoria of the other genera of the Erysipha- 

 ceae. With the exception of these special branches and of the 

 haustoria, the mycelium of all our species in the group is exter- 

 nal to the tissues of the host. — However Salmon in his studies 

 on the group has pointed out that in Erysiphc tanrica the myce- 

 lium which produces the conidiospores is endophytic, and the 

 conidiophores emerge singly or in groups through the stomata. 

 The conidiophores are also sometimes branched, another char- 



60 



