OF THE UNITED STATES. 7 



orange colored masses, which are supposed by many to be the flowers of the cedar-trees. 

 Probably in no part of the world are the species so abundant as in the eastern United 

 States, and material for study can be procured in the greatest abundance. In one 

 respect this abundance has its advantages, in another it has its disadvantages. The 

 Gymnosporangia of Europe, compared with our own, are few in number and much less 

 abundant, the number of species found in central and northern Europe being limited by 

 Oersted and Reess to three. Oersted, of Copenhagen, was the first to study their devel- 

 opment. He connected the gelatinous teleutosporic stages which occur on species 

 of Juniperus with the elongated cluster-cups placed formerly in the genus Roestelia, which 

 are found in summer on the leaves of different Pomeae, thorns, pears, apples, etc. He 

 went so far as to connect each of the three species of Gymnosporangium found in Denmark 

 with a particular species of Roestelia. The experiments of Oersted consisted in sowino" 

 the germinating sporidia of the Gymnosporangia on leaves of different Pomeae. I shall 

 have occasion to return to this subject later, but it is sufficient to notice in this connection 

 that Oersted's ^ observations were afterwards confirmed by De Bary^and others in Ger- 

 many, Cornu^in France, and Cramer* in Switzerland, and accordingly the genus Roestelia 

 has been suppressed by recent continental writers, who refer to the species formerly placed 

 in that genus as the aecidial or hymeniferus stage of the different Gymnosporano-ia. 



If one then would study the American species of Gymnosporangium in the light of 

 modern research, he must also take into account the different Roesteliae of which we have 

 an abundance. The first step is to settle the species of the two genera on anatomical 

 grounds, and then by cultures or observations in the field to ascertain their genetic rela- 

 tions. I insist on the importance of first defining the species from their anatomical struct- 

 ure, for unless this is done any cultures which may be made can have very little value and 

 one is constantly groping in the dark. One may afterwards modify his view of the species 

 in consequence of knowledge derived from artificial cultures, but one should not, for 

 instance, conclude at once, because the sporidia of a given species of Gymnosporano-ium 

 produce spermogonia when sown on the leaves of two plants which are known to have 

 Roesteliae differing in their morphological characters, that the two Roesteliae are the same 

 species in spite of their different ajjpearance. In determining the species of the two 

 genera one is obliged to ascertain which of our species are the same as those found in 

 Europe, and here a difficulty arises, for one is not quite sure in some cases how far a Euro- 

 pean species of fungus may vary from the type when growing upon a different host from 

 the one on which it occurs in Europe. In this case one would gladly resort to artificial 

 cultures to settle the question. Unfortunately for us who are obliged to follow in the 

 steps of Europeans in so far as the determination of species common to both continents is 

 concerned, European writers have not agreed amongst themselves as to the limits of 



^Bot. Zeit., 1865, 291 ; and 1867, 222. Nouvelles obscrva- tesvampe og navolig om dea genetiske Forbindelse raelleia 



tions siir un champignon parasite doat les generations alter- Sevenbommens Baevrerust og Paeretraeets Gitterrust. 



nantes habitent sur deux plantes hospitalieres differentes. Copenhagen, 1868. 



Bulletin de I' Academie Royale des Sciences do Copenhague, ^ Bot. Zeit., 18G5, 222. 



1866. 'Bull Soc. Bot. Tome 25, pp. 122, 221, &c. 



Nouveaux essais de se^nis faits avec des champignons par- * Ueber den Gitterrost der Biriibaumo and seine Bekamp- 



asites. Loc. clt., 1867. fung. Schweizer. landwirthschaft Zsitschrifc. Solothurn, 



Om en saeregen, hidtil ukjendt UJvikling hos visse Snyl- 1876. 



