[Vol. 10 



152 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



condition is suggested by the fact that the spores at the margin 

 and on the surface of the water drop are often the only ones 

 which germinate. Very seldom does germination occur uni- 

 formly throughout a drop of spore suspension and then it is 

 only when the drop is small or spread out as a thin film. 



Pycnospores may endure severe desiccation without losing 

 viability if allowed to dry on the beaks of the pycnidia. When 

 first exuded, the spore balls are merely a dense suspension of 

 pycnospores which quickly disperse by diffusion when placed in 

 water. With loss of water the droplets become, first, doughy in 

 consistency, and finally, as desiccation proceeds, much smaller, 

 hard, and very dry. In this air-dry condition they do not 

 separate readily, and considerable difficulty is experienced when 

 one attempts to dissolve them in water. Spores in various states 

 of dryness may be obtained from the same culture if long pieces 

 of soybean petiole in test-tubes provided at the bottom with 

 moist cotton are inoculated at the top. Pycnidia develop first 

 at the upper end and exude spore droplets which, perched on 

 the tips of the beaks, dry rapidly, while at the bottom, where 

 the water supply is maintained by the moist cotton, pycnidia 

 continue to exude spores for a much longer time. Germination 

 tests have been made, using spores a few hours after they had 

 exuded, when they were in the doughy condition and when they 

 had become air-dry. In such a test, where spores in all 3 of 

 the conditions cited above were taken from a 53-day-old culture 

 and put into tap water on depression slides, the germination was 

 approximately 50 per cent of the total for spores in all 3 conditions. 

 In another trial with spores from a culture of the same age and 

 strain, spores from a droplet which had recently exuded gave 

 approximately 100 per cent germination, while air-dry spores 



taken from a spore droplet which had shrunk to about one-fourth 

 its original size and had changed to the reddish brown color 

 commonly assumed by spore balls in the air-dry condition, gave 

 only 5 per cent germination. At another time, spores were taken 

 from a culture 61 days old which had been kept in a wire basket 

 and had become thoroughly dry. These spores gave 90-100 

 per cent germination in a mineral nutrient solution. In one 

 instance, 25 per cent germination was obtained by use of spores 



