CULTUEAL CHARACTERS OF CHESTNUT-BLIGHT FUNGUS. 17 



mata, with spores extruding in thick, elongated masses. E. radicalis 

 mississippiensis appears somewhat intermediate between E. para- 

 sitica and E. radicalis in regard to the character and abundance of 

 the pycnidia and in color of the growth. These peculiarities have 

 been very uniform and constant in all the cultures on this medium, 

 and if they could be coordmated with regular morphological differ- 

 ences in nature would justify its separation as a species. 



SUMMARY. 



The chestnut-blight fungus Endothia parasitica has three rather 

 close relatives, E. radicalis (E. virginiana And. and And.), E. radi- 

 calis mississippiensis, and E. gyrosa (E. radicalis of Clinton), which 

 in their pycnidial condition are not readily distinguished with cer- 

 tainty by either macroscopic or microscopic examination. 



Physiological studies of these organisms in pure cultures have 

 been made to test their relation to light, moisture, and temperature, 

 and also their behavior on different culture media. All behaved the 

 same in light and darkness, growing about equally well in either. 



Cultures of Endothia parasitica and E. radicalis were made on 

 corn meal to which different quantities of water had been added. 

 The cultures with equal quantities of corn meal and water produced 

 pycnidia and spores more abundantly than those to which the greater 

 quantities of water were added. 



Temperature tests showed that 8° to 9° C. is the least temperature 

 at which any of the three species will grow. The highest temperature 

 at which growth occurred was 35° C. for Endothia parasitica and E. 

 gyrosa, and 32° C. for E. radicalis. The best temperature for growth 

 was between 18° and 28° C. for all. 



Studies of over 2,000 pure cultures of these fungi appear to show 

 that they possess constant and easily recognized cultural characters 

 on several culture media, of which potato agar and corn meal are 

 the best that have been tried. 



The most distinctive and reliable cultural character of Endothia 

 parasitica is the peculiar, granular, glistening light orange-colored 

 surface growth produced at the bottom of potato-agar slants. This 

 usually appears within a week. None of the other organisms have 

 developed this character, though E. radicalis occasionally in very old 

 cultures shows suggestions of it. The orange color of the mycelium 

 of E. parasitica as seen by transmitted light usually appears in three 

 or four days, and this is ordinarily sufficient for identification. In 

 the other species this color is not produced at all, or in case of E. 

 radicalis not until a few days later. 

 98858°— Cir. 131—13 3 



