CULTTTEAL CHARACTERS OF CHESTXUT-BLIGHT PUiS^GUS. 11 



much more striking on unslanted tubes. Upright tubes have the 

 disadvantage of a small surface, but this is more than offset by the 

 fact that the greater depth of agar gives a much more uniform 

 moisture supply to the fungus. The most characteristic differences 

 upon this medium appear in cultures from 6 weeks to 2 months old. 

 The earUer stages are also sufficiently distinct for easy identification. 

 In the older stages EndotJiia paraMtica showed a scant white growth 

 of surface mycehum with several prominent pycnidial pustules clus- 

 tered near the center and of a slightly darker shade than the raw sienna 

 of Ridgway. E. radicalis, on the other hand, produced a rather 

 abundant deep chrome mycelium with usiially one or two smaller. 

 less conspicuous pycnidial pustides. E. radiealis mississippiensis on 

 this medium resembled E. parasitica in producing only a very scant 

 surface growth of mycehum. but the color was between cadmium 

 yeUow and raw sienna. The pycnidial pustules were more numerous 

 than in E. radicalis and smaller and more scattered than in E. para- 

 sitica. 



At this age Endothia gyrosa showed rather abundant, felty white 

 mycelium flecked with capucine buff but no pycnidia. Occasionally 

 in old cultures of this species small pycnospore threads were pro- 

 duced. On corn-meal agar — 15 the growth was slow, but an abund- 

 ance of spores was produced. 



CITLTTJBES ON POTATO AGAR. 



The formula for the potato agar used is as follows: 

 Put clean pared potatoes through a meat grinder. To 1.000. grams 

 of the potato pulp add an equal quantity of distilled water. Stir 

 thoroughlv and let stand in an ice box for an hour, with occasional 

 stirring. Strain through gauze of medium mesh. Make up to three 

 times the weight of the original pulp with distiQed water. Steam for 

 1 hour, filter through cotton and paper, and make up to 3.000 cubic 

 centimeters with distilled water. Add 1^ per cent of agar flour, 

 steam for 1 hour, filter through cotton and paper, tube, and autoclave 

 for 15 minutes at 115° C. 



In practice it was found that the potato agar prepared according to 

 this formula varies widely in acidity and probably in some other 

 respects. To reduce this variation a large quantity of potato juice 

 was made from a uniform lot of Burbank potatoes. This was placed 

 in 1 ,000-cubic-centimeter flasks, tightly plugged and kept in a refriger- 

 ator. The juice was then made up into agar tubes as needed. It 

 was found that this agar varied less than 1 per cent in acidity, 

 changing from -t-7 to -1-6 durmg .3 months. 



Endothia parasitica. — Pycnospore streaks of EndotJiia parasitica 

 and E. radicalis on this potato agar agreed closely with that described 



[Cir. 131] 



