31-4 PROCEEDINGS OF THE AMERICAN ACADEMY 



Comments on Cultures I. -V. — The cultures I.-III. were started on 

 the same day. No. IV. was not started until the following day, as a 

 microscopic examination showed that the spores were not germinating 

 freely until May 19th. In No. V. the sporidia were not produced in 

 sufTicient quantity for sowing until May 23d, and even then they 

 were scanty, so that fresh specimens were collected, which produced 

 a sufTicient quantity of sporidia for sowing on May 29th. At the time 

 when the five cultures were started, the only seedlings of a suitable size 

 which could be procured were those of apple ; but as it was easier to 

 obtain pure spores of the species of Gymnosporangium on the date 

 named, the cultures were then started, and a second series of cultures 

 were arranged later, when other seedlings could be procured. The 

 spores for the second series were from specimens selected with care, so 

 as to be as pure as possible ; but from the later date, and the fact that 

 there had been showers which had swollen the masses of spores, the 

 possibility of the accidental mixture of the spores of one species with 

 those of another could not be guarded against with the same degree of 

 certainty as in the preceding series. It may be remarked that in 1883 

 the season was backward, and the Gymnosporangia did not mature as 

 early as they frequently do. In both series of cultures the control 

 plants remained free from spermogonia. Where the statement is 

 above made, that the cultures were abandoned on a given day, it should 

 be understood that the statement applies only to the leaves under bell- 

 glasses. In the cases where spermogonia appeared on the leaves of 

 seedlings, the cultures were kept for a longer period ; but these cases 

 will be referred to again later. 



VI. Gym. fuscum var. globosum. 



May 25. Sporidia sown on 



2 seedlings of Cratcegiis Douglasii. 



1 seedling of Pgrus sp. cult. 



May 31. Spermogonia appeared on all the seedlings. 



VII. Gym. macropus. 



May 25. Sporidia sown on 



2 seedlings of Crattegus Douglasii. 

 1 seedling of Pgrus cult. 



June 5. Spermogonia appeared on one Crataegus. 



