REED: SPECIALIZATION OF PARASITIC FUNGI 377 



1, Euphorbiae-didcis s. str. on Euphorbia diilcis. 



2. Euphorbiae-strictae W. Muller on Euphorbia stricta and E. platy- 



phyllos. 



Melampsora populina Lev. and Melampsora Tremulae Tul. A 

 number of different species of Melampsora are recorded as having their 

 uredo and teleuto stages on the various kinds of poplars. These rusts, 

 however, constitute a group of closely related forms and differ but 

 little in their structural characteristics. The main differences appear 

 to be in the choice of hosts, especially in the aecidial stage. 



The relationships between the poplar rusts may best be indicated 

 by grouping them under the above names. Melampsora populina 

 is distinguished from M. Tremulae by the fact that the teleutospores 

 are subcuticular while in the case of M. Tremulae they are subepidermal. 

 The uredo and teleuto hosts are also different species of Populus and 

 serve further as a means of distinguishing between the two. Klebahn 

 (87, 91) has made a special study of these rusts. 



Melampsora populina includes two rusts which can be distinguished 

 only by the choice of the aecidial host. These are: 



1. Melampsora Allii-populina Kleb.; aecidial stage on Allium cepa 



and A. ursinum; uredo and teleuto stages on Populus balsamif- 

 era and P. nigra. 



2. Melampsora Larici-populina Kleb.; aecidial stage on Larix decidua; 



uredo and teleuto stages on Populus balsamif era and P. nigra. 



Melampsora Tremulae includes four or five rusts whose uredo and 



teleuto stages occur on Populus alba and P. tremtda, rarely on other 



species; the aecidial stage is found on widely separated host plants. 



The following belong in this group: 



1 . Melampsora Larici-Tremidae Kleb. ; aecidial stage on Larix decidua. 



2. Melampsora pinitorqua Rostr.; aecidial stage on Pinus silvestris. 



3. Melampsora Rostrupii Wagner; aecidial stage on Mercurialis 



perennis. 



4. Melampsora Magnusiana Wagner; aecidial stage on Chelidonium 



major. 



5. Melampsora Klebahni Bubak; aecidial stage on Corydalis cava, C. 



digitata, C. fabacea, C. laxa and C. solida. This may not be 

 distinct from the preceding one. 

 Melampsoras of Salix. The Melampsoras on different species of 

 Salix constitute a complex group of interrelated rusts. The structural 

 differences between the large number of commonly recognized species 

 are comparatively insignificant. In order to segregate the different 

 species it is necessary to rely, to a large extent, upon differences in 

 the choice of host. The willow rusts also afford many parallels among 

 the poplar rusts and in some cases it is not possible to distinguish the 

 rusts on these two genera except by the choice of host. 



