ARTHUR AND JoHNsTON: UREDINALES OF CUBA 107 
the number of species in each genus, as well as in the comparative 
numbers of long- and short-cycle forms. The differences are only 
such as might be expected from incomplete exploration. The 
greater total number of species now known for Porto Rico is 
chiefly accounted for by the greater number of unconnected 
Uredo-forms, which have been found in that island. Whether 
this array of forms still under the genus Uredo indicates that the 
flora of Porto Rico is more tropical than that of Cuba, or whether 
it is better known for such forms, is doubtless debatable. 
A comparison of the Cuban with a continental area presents 
marked differences. The most instructive comparison at present 
possible is that with Guatemala. A recent study of the Uredi- 
nales of Guatemala, not yet published, gives a list of species about 
as complete for that country, as that here presented for Cuba. 
Nearly a third of the area of Guatemala, especially the northern 
part in the Department of Peten, is unrepresented by collections. 
The remainder of the country is of about the area of Cuba, but of a 
more varied topography, having many high mountains. The 
climate is doubtless somewhat more tropical that that of Cuba, 
although northern species find congenial conditions in the high 
altitudes. Thus the genera Melampsora, Melampsoridium, Puc- 
ciniastrum, Uropyxis, and Phragmidium, not represented in Cuba 
or Porto Rico, are to be found there. Also the forms under Uredo 
are only about one half those in Cuba and one third those in Porto 
Rico. Both classes of facts indicate certain less tropical aspects 
of the flora, but nevertheless, they are aspects that may have to do 
with the boreal features of the mountainous part of the flora. 
There are, however, three genera, that is, treating the correlated 
Uromyces and Puccinia as a single genus, which can be taken as 
comparable factors to indicate differences between the insular and 
continental floras. 
NUMBER OF SPECIES OF RUSTS 
| Cuba Porto Rico Guatemala 
ecd Eu oc уу a Pte AER E | 5 3 8 
Nia... d. dl aida d mere k^ 9 то 20 
ы а оо oorr | 76 74 150 
