26 



Mycologia 



We have shown that the percentage of germinating spores in 

 our cultures of Aecidium myricatum is very low, yet one can find 

 germinating spores in the drops of water on the leaves of cedars 

 that have been sprayed and kept in the infection chamber twenty- 

 four hours. The results of a number of test experiments are 

 given in Table I. Tap water was used in all cases. 



Table I. Shows the approximate percentages of germination 

 of aecidiospores of Gymno sporangium myricatum in water cul- 

 tures. 



Date 



Method 



No. Tests 



No. Positive 

 Results 



Approximate 

 Percentage of 

 Germination 





Hanging drop 



19 



O 



0 



" 28, " 



Petri dish 



5 



0 



0 







12 



O 



0 



Mar. 10, 1916 





6 



0 



0 





Watch glass 



2 



I 



.4% 







6 



6 



.3% 



" 16, " 



Petri dish 



3 



3 



.5% 



" 16, " 



Watch glass 



6 



5 



.2% 





Hanging drop 



6 



0 



0 





Watch glass 



6 



6 



•5% 



" 20, " 



Petri dish 



3 



3 



1.0% 



" 25, " 



Watch glass 



3 



3 



•5% 



Where spores are floated on water in watch glasses or Petri 

 dishes a low percentage of germination was obtained. In several 

 cases in which watch glass tests of aecidiospores of both G. myri- 

 catum and G. clavariae forme were made, the glasses were stacked 

 on one another, and it was found that the spores in the uncovered 

 dish germinated sooner and usually with a higher percentage. 

 The Petri dishes were always set in the damp chamber, and with- 

 out cover, so that there was an unlimited supply of air. Under 

 these favorable conditions the spores begin to germinate within 

 six or eight hours. Leaves bearing aecidia had been placed in 

 cheesecloth bags and hung outside the greenhouse all winter; 

 spores from these leaves did not germinate in Petri dish cultures 

 when tried the following March, as shown in the above table. 



In June, 191 6, germination tests were made of aecidiospores of 

 several other species of Gymno sporangium. There is the greatest 

 variation in the behavior of the different species. G. globosum 

 showed the lowest percentage, not over 0.1 per cent.; G. juvenes- 

 cens up to 10 per cent. ; G. nidus-avis occasionally as high as 5c 



