38 



BULLETIIsr &57, U. S. DEPARTMENT OF AGEICULTUEE. 



pine bearing secia. It was placed in a box in the laboratory and 

 allowed to dry out. Tests were made by inoculating leaves of Ribes 

 nigrum plants on May 7, May 21, June 4, and June 23. On the last 

 date no infection occurred. In 1916, McCubbin repeated these 

 experiments and found that the seciospores remained capable of 

 infection under the conditions of his experiment at least 39 days. 

 He believes they may retain viability considerably longer, as his 

 tests were conducted under adverse conditions. 



yEciospores collected on April 9, 1917, and kept in a closed glass 

 vial were tested by Gravatt weekly in hanging drops of distilled water. 

 They gave good germination for about one month, then weakened 

 untn June 9, when the last germination occurred. The tests con- 

 tinue4 until July 14. On May 7, 1917, another series of similar tests 

 was started by Gravatt and Taylor. (See Table II.) The aeciospores 

 were placed in two glass vials with cheesecloth tied over the tops. 

 One vial (B) was kept out of doors on a window sill on the north 

 side of a building where the sun did not shine. The other vial (A) 

 was kept in a dark refrigerator. The spores were tested weekly in 

 distilled water. In most cases the cultures were placed in an ice 

 box for about 12 hours. The spores kept in the ice box retained 

 their color throughout, while those on the window sill had faded 

 perceptibly by June 16. Lot A varied in germination from 8 per 

 cent at first to 3 per cent on June 2. Germination persisted until 

 July 2, when the last occurred in this lot. Lot B germinated freely 

 until May 26 and not at all after June 23. Cooling and darkness in 

 this case decidedly stimulated germination for one month and pro- 

 longed viability about 10 days after the uncooled aeciospores which 

 were exposed to light had lost all viability. 



Table II. — Longevity of the spores of Cronartium ribicola. 





Germination (per cent). 





Date, 

 1917. 



Lot A, vial in 

 refrigerator. 



Lot B, vial out of 

 doors. 



Notes. 





^cio- 

 spores. 



Uredi- 



nio- 

 spores. 



Telio- 

 spores. 



Maio- 

 spores. 



Uredi- 

 . nio- 

 spores. 



Telio- 

 spores. 





May 8. 

 May 12. 

 May 19. 

 May 26. 

 June 2. 

 June 9. 

 June 16. 

 June 23. 

 July 2. 

 July 7. 

 July 14. 



8 

 8 

 5 

 4 

 3 

 1 



.1 

 



.05 

 

 



13 

 10 

 60 

 45 



6 

 .65 



1.35 



















90 

 85 

 80 

 70 

 40 

 51.3 



4.5 



3.5 

 .5 











8 

 1 

 2 

 3 



.8 



.1 

 



.05 

 

 

 



8 



10 



40 



37 



.8 



1.5 









 .1 











85 

 90 

 85 

 50 

 10 



4.4 











Not cooled in refrigerator before germination. 

 Do. 



Lot A somewhat faded. 

 Lot A much faded. 

 Teliospores in lot A mouldy. 



iEciospores and urediniospores mouldy in 

 lot A, color of lot B still fairly good. 



