May6, i9i8 YelloTV-Lcafbloick of Alfalfa 321 



When pure cultures had been obtained, efforts were resumed under 

 more favorable conditions. Germination was attempted in poured 

 plates, on an agar surface, in distilled water, and in several liquid media 

 at temperatures within the range through which the mycelium of the 

 fungus grows. A few doubtful cases of germination have been noted in 

 which it could not be determined whether a structure attached to a 

 spore w^as an attached conidiophore or a germ tube. But since the struc- 

 ture did not develop beyond the length of a normal conidiophore, it was 

 assumed to be such. 



The nearest approaches to germination have been observed in the case 

 of spores flooded on a plate of potato agar, the culture medium upon 

 which the fungus grows best. In early tests it appeared that a single 

 spore sent out a lateral germ tube about 20 p. in length. Later, occa- 

 sional spores on this substratum have shown a slight bulging of the cell 

 wall, but no well-defined germination has taken place. In order to 



allow conidia a long time in which to develop 

 fungus colonies, they have been flowed in a 

 water suspension on agar slopes in test tubes. 

 The free water was poured off and the tubes 

 were set aside for several weeks ; but no fungus 

 colonies developed upon them. 



Conidia upon dead leaves have been included in 

 Fig. 6.— PyTencpc2i:a medicaginis: germination tcsts, but not cnough of over-win- 



Germinating ascospores. • i • i 



tered comdia have been secured for this purpose. 

 These results, together with the fact that no successful inoculations 

 with conidia have been made, make it seem unlikely that they 

 germinate often, at least not in significant numbers. 



GERMINATION OF ASCOSPORES 



Ascospores of Pyrcnopeziza medicaginis germinate readily on an agar 

 surface, or in distilled water, but very poorly, if at all, when they are 

 submerged in poured agar plates. The percentage of germination is 

 very variable, usually being rather low, from 25 to 30 per cent but 

 sometimes being as high as 80 per cent. No explanation for this varia- 

 bility can be offered. The spore germinates from any part of its cir- 

 cumference with little apparent preference for the side or the end (fig. 6). 

 The germ tube is soon cut off by a septum. Other features of germi- 

 nation will be discussed under temperature relations. 



Relations of Temperature 

 growth op mycelium 



In order to determine the optimum temperature for the development 

 of mycelium, transfers were made on potato agar and placed at tempera- 

 tures ranging from 2° to 29° C. These were kept under observation for 



