OF THE UNITED STATES. 



35 



G. clavipes on 3 leaves of Amelanchier. No result. 



Notk. The cultures of 1870 were made at the laboratory of the Busscy Institution. Those made in June 

 continued only 17 days, but no result being then obtained the laboratory was closed for the season. 



IV. May, 1877. 



G. macropus on 3 leaves of apple, 3 of Amelanchier, 3 of Crataegus tomentosa, and 3 



of Pyrus arbutifolia. Spermogonia appeared on one leaf of Amelanchier and one of 



C. tomentosa in ten days. 

 G. globosum on 3 leaves of apple, 3 of Amelanchier, 3 of Crataegus tomentosa, and 3 of 



Pyrus arbutifolia. Spermogonia appeared on all the leaves of Crataegus. 

 G. biseptatum on 3 leaves of Crataegus tomentosa, 3 of apple, 3 of Amelanchier, and 3 



of Pyrus arbutifolia. Spermogonia appeared on one leaf of Crataegus in six days. 

 G. Ellisii on 3 leaves of apple and 3 of Amelanchier. No result. 



Note. The cultures of 1877 were made at the Bussey Institution, and lasted from May 25th to July 4th. 



V. June, 1878. 



G. macropus on 3 apple leaves, 3 of Crataegus oxyacantha, 3 of C. crus-galli, and 3 

 of pear. No result. 



G. Ellisii on 3 apple, 3 pear, 3 C. oxyacantha and 3 C. crus-galli leaves. No result. 

 G. biseptatum on 3 apple, 3 pear, 3 C. oxyacantha and 3 C. crus-galli leaves. No 

 result. 



G. globosum on 3 pear, 3 C. oxyacantha, 3 C. crus-galli, and 1 apple leaf. No result. 

 VI. 



G. Ellisii on two pear seedlings and on two young plants of C. tomentosa. No result. 

 G. macropus on an apple seedling and 2 plants of C. tomentosa. No result. 



Being absent from Cambridge in 1879, no cultures were made, and the cultures of 1880 

 present no result worth detailing, as no spermogonia were produced. 



In reviewing the record given above, one is struck with the small number of cases in 

 which spermogonia succeeded the sowings on the different Pomeae. Certainly a sufficient 

 variety of leaves was selected, for it is on Amelanchier, Crataegus, Pyrus arbutifolia, and 

 cultivated apples and pears that the greater part of our Roesteliae are found in nature. 

 That the sporidia used were in good condition was shown by microscopical examination. 

 In running over the list, it is seen that the only plants on which spermogonia were pro- 

 duced were Crataegus tomentosa and Amelanchier canadensis. Those on Amelanchier 

 followed the sowing of the spores of G. macropus, but, inasmuch as three species of Roes- 

 telia are known on that plant, it is impossible to say to which the spermogonia belonged. 

 What is surprising, however, is that of the three species of Gymnosporangium which 

 were followed by spermogonia on C. tomentosa, viz.: G. macropus, G. globosum, and G. 

 biseptatum, not one is the species which, according to Oersted, ought to produce our com- 

 mon form on C. tomentosa, namely P. lacerata. Accepting his view one would hardly 

 have been led to expect spermogonia on such a host plant from three species so distinct 

 from G. clavariaeforme. Further, we are not allowed to suppose that the production of 

 spermogonia on C. tomentosa indicates any close resemblance between the three different 

 Gymnosporangia. It might, perhaps, be said, considering how much more frequently the 

 spermogonia followed the sowing of G. globosum than of the other two species, that 

 where the spermogonia appeared to follow the latter, it was really because some of the 



