UREDINALES 91 



ous wild plants. Of the species of Gymnosporangium, which 

 produce cedar-apples or other deformities on Juniperus we have 

 already spoken ; six species are found on Juniperus Virgin- 

 tana * alone ; other species are found on J. communis, J. occidi n- 

 talis, and Chamaecyparis thyoides. 



The genera found in the United States may be distinguished as 

 follows : 



1. Teleutospores imbedded in masses of jelly, mostly 2-celled; (parasitic on 



Cupressinae ) . GYMNOSPOR ANGIUM. f 



Teleutospores in definite sori, not imbedded in jelly. 2. 



2. Teleutospores with a simple stalk which is occasionally obsolete. 3. 

 Teleutospores united in cushion-like bodies formed of several or many 



cells ; stems formed of several united or separate stalks. RAVENELIA. 



3. Teleutospores I -celled. UROMYCES.f 

 Teleutospores normally 2-celled. 4. 

 Teleutospores 3-several- celled. 6. 



4. Endospore of teleutospores becoming mucilaginousand swollen. 



UROPYXIS. 

 Endospore of teleutospores without a mucilaginous layer. 5. 



5. Aecidia without a pseudoperidium ; spermogones spherical ; (a single 



species parasitic on Rubits}. GYMNOCONIA. 



Aecidia, when present, with a pseudoperidium, often wanting. 



PUGCINIA.f 



6. Septa at right angles to the axis of the spore. 7. 

 Septa 3, uniting in triangles. TRIPHRAGMIUM. 



* Cf. Underwood Earle. The Distribution of the Species of Gymno- 

 sporangium. Bot. Gaz. 22 : 255-258. 1896. 



f Among the unfortunate features connected with systematic study are the 

 troublesome questions of synonymy and priority. As in many other things, 

 we of the present generation suffer from the lack of system of the genera- 

 tions behind us. Asa Gray stated succinctly the basis for the difficulty : 

 " For each plant or group there can be only one valid name and that 

 always the most ancient if it is tenable." Now, it is claimed, Micheli 

 in 1729 established the genus Puccinia for a gelatinous parasite of the 

 Juniper (= Gymnosporangium as used above), and Adanson in 1763 

 adopted this use of the name long before it was diverted to its present usage. 

 If these are the real facts, Puccinia may have to replace Gymnosporangium 

 as an older name. In a similar way Dicaeoma may have to stand for Puc- 

 cinia,. Caeomurus for Uromyces and Aregma for Phragmidium. This is 



