120 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 10 



From culture on soybean stem 15 days after inoculation: 

 6.0-9.0 X 1.8-2.7 pi, average 6.91 X 2.18 pu 



From cooked sweet potato four months after inoculation: 

 5.0-7.6 X 1.9-2.7 [x, average 5.79 X 2.28 pu 



The averages noted above were of 50 measurements in each 

 case, and all measurements were made after the pycnidia had 

 reached maturity as indicated by exudation of pycnospores. 

 The spores were mounted in water and an oil-immersion objective 



was used in measuring. Spores from 



pycnidia which developed on pods in 



moist chambers averaged larger than 

 when developed under drier condi- 



stems in the 



house 



As noted above, pycnospores escape 

 through a pore and collect in milky- 

 colored droplets at the tips of the 

 beaks of the pycnidia, from which they 

 are readily splashed by rain. In cul- 

 Fig. 3. Pyrn. pores of soy- ture these droplets slowly dry down, 



bean fungus, germinating. , . „ i X « 



becoming yellow and finally some 

 shade of brown. On cultures on soybean stems and petioles, on 

 stems of Melilotus alba, and on pods in a moist chamber pycnidia 

 develop and exude spore droplets in 11-13 days when kept at 

 summer temperature in light. If these cultures are prevented 

 from dying out, this may continue for several months. Several 

 cultures on stems of Melilotus alba, inoculated August 10, 1921, 

 and kept in a covered glass dish, began exuding pycnidia on the 

 thirteenth day and were still doing so on December 13, 1921, 91 

 days after inoculation. 



Under appropriate conditions, pycnospores begin to germinate 



hours after being placed 



take 



water and enlarge noticeably, after which one or two slender, 

 hyaline germ tubes are formed. At room temperature during 

 summer, the longest of these tubes may reach a length of 4 to 

 5 times that of the spore in 18 hours. The guttulae disappear 

 and the tubes continue to grow for about 48 hours. Germ 

 tubes formed on the surface remain long, slender, and soarselv 



