INTRODUCTION. XXIX 
The species are all included between the 70th and 
20th degrees of Northern latitude; except the R. Mon- 
tezume of Mexico, found in 19° N. at an elevation of 
more than 9300 feet above the level of the sea. But 
Baron Humboldt has calculated that in tropical coun- 
tries the decrement of caloric is one degree every 90 
toises of vertical elevation; therefore the heat at this 
height would be nearly the same as that of countries 
29° further from the equator; so that its situation is 
essentially the same as that of the principal European 
parallel, to the species of which it is more nearly re- 
lated than to those of its own continent. 
In Asia half the species have been found. Of the 
thirty-nine which it produces, eighteen are natives: of 
the Russian dominions and the countries adjacent. 
Most of these are very similar to the European portion 
of the genus, and five are common both to Europe and 
to Asia. Of the remainder, one, which is perhaps a 
distinct genus, has been discovered in Persia, fifteen in 
China, and two of the latter with four others in the 
North of India; one of which has considerable affinity 
to the R. moschata of Northern Africa. The Chinese 
and Indian species have an habit entirely different from 
the rest; but R. sericea and macrophylla of Gossam 
Than exhibit in some measure the appearance of both. 
It is from Asia, which may indeed be called “ the land 
of the Rose,” that the greatest number of novelties are 
to be expected. With the Roses of the Crimea we are 
entirely unacquainted, and yet they are said to grow 
there in the most astonishing profusion. Mr. Moor- 
croft met with small rose-bushes at Niti, in latitude 
30° 50’ N. just coming into leaf on the 9th of June; 
