OF ARTS AND SCIENCES. 261 



locality was especially favorable for the purpose, being some miles 

 from the nearest cedars, and tljis, together with the fact that only sucli 

 leaves and shoots were infected as had developed after the plants were 

 brought to Boston, went far to diminish the chance of accidental in- 

 fection from outside sources. 



Four rooms were at my disposal, and it was thus possible to guard 

 against any mixture of the Gymnosjiorangia employed. A number of 

 control plants were also used, and, by making the intervals between 

 successive sowings suthciently great, plants subsequently infected were 

 made to serve a similar purpose. The Gymnosporangia used included 

 all the species found in this vicinity ; namely, macropics, clavariceforme, 

 globosum, hiseptatum, Ellisii, clavipes, and conicum. All of these, with 

 the exception of El/isii, mature at about the same time, generally 

 during the first week in May ; and a supply of branches bearing the 

 distortions peculiar to the various species was gathered in April, before 

 the sporiferous masses had been protruded by rains, and kept apart in 

 water for the subsequent sowings. 



The method of infection was as follows. Unexpanded sporiferous 

 masses were put in watch-glasses with a little water, and these placed 

 in a moist chamber, a common jelly tumbler filled with wet sphagmmi 

 being found convenient for this purpose. In from twelve to eighteen 

 hours the teleutospores had as a rule produced an abundance of spo- 

 ridia in the water and on the surflice of the expanded masses. The 

 latter were then torn apart, and placed directly upon the plants to be 

 infected, which were first thoroughly sprinkled, and after infection 

 kept, when practicable, under bell jars or cones of wet paper for about 

 twenty-four hours ; after which they were uncovered and repeatedly 

 sprinkled. The results obtained seemed better where portions of the 

 jelly were applied, than when water with sporidia in suspension was 

 employed ; but in the former case it is necessary to remove the dried 

 membrane that remains, which otherwise injures the tender leaves. 



In view of the theory that the spermatia are sexual in function, and 

 fertilize a female organ, the trichogyne, which subsequently gives rise 

 to the aecidium, a " fertilization " was attempted by collecting the exu- 

 dations from the spermogonia in a drop of water, and painting them 

 upon the under side of different leaves in plants infected by the same 

 species. This was carefully followed up with G. globosum, wiihout 

 resulting in the production of any oscidia, and in two instances where 

 aecidia were obtained ( G. hiseptatum and macropus) no such fertiliza- 

 tion was attempted, thus giving no definite result for or against the 

 sexual theory. It should be mentioned that small flies were repeatedly 



