Weir & Hubert: Melampsorae on Populus 195 



species of Melampsora on leaves of the same host and included 

 in one collection. In order to check the results obtained from 

 sowing sporidia of M. medusae (collection No. 24) on Pseu- 

 dotsuga species the aeciospores thus obtained were sown on 

 young leaves of Populus trichocarpa. The leaves were inoculated 

 May 18 and uredinia appeared June 8. Successful inoculations 

 have been secured by sowing some of these urediniospores upon 

 leaves of Populus trichocarpa. Inoculation's were made on June 

 9, 1 91 7, and on June 20 abundant uredinial sori were produced. 

 This explains the great abundance of these rusts in regions of few 

 aecial hosts. The proper conclusion of this culture will be to use 

 the telial stage in producing the rust on Larix. 



Aeciospores resulting from a successful inoculation with col- 

 lection No. 57 on Larix occidentalis were sown June 29, 191 7, on 

 young leaves of Populus trichocarpa. Uredinia developed in 

 abundance on July 7. No marked differences could be found be- 

 tween the uredinia and urediniospores of this culture and those 

 resulting from an inoculation of P. trichocarpa leaves with aecio- 

 spores from Pseadotsuga taxifolia. 



A careful study of the pycniospores and aeciospores resulting 

 from the above cultures was made. These aeciospores on species 

 of Larix and on species of Pseudotsuga were also compared with 

 aeciospores on Larix laricina resulting from an inoculation with 

 telia of Melampsora medusae from Populus deltoides and P. 

 tremuloides cultured by Mains at Ann Arbor, Michigan, May 14, 

 1914 (N. A. U. No. 1 121). No important differences could be 

 found in comparing the characteristics of these spores. Repeated 

 attempts have been made to find evident differential characters 

 by which the uredinia and telia of these two forms here consid- 

 sidered may be plainly and readily separated,- but with very little 

 success. The first noticeable gross character of M. albertensis is 

 that the telia appear to spread out like melted wax while those 

 of M. medusae (Fig. 1) are more elevated and conspicuous. The 

 former character of M. albertensis only holds good, however, 

 where average-sized leaves of its most common host, viz., Popu- 

 lus tremuloides are infected. The rust has been repeatedly col- 

 lected from large leaves from sprouts at the base of trees which 



