KVi INTRODUCTION. 
It is the only genus of Jussieu’s second section of 
‘Rosacea#, and is distinguished from the succeeding 
sections of that order, by its fleshy urceolate calyx, 
and hairy, osseous pericarpia. From PomMacez there 
is no absolute mark of distinction, except its solitary 
suspended ovulum, and indefinite ovaria; for, however 
sufficient the distinction may at first sight appear, be- 
tween the fructus inferus of the latter and superus of 
RosacE#, it is almost entirely removed by Crategus 
glabra and arbutifolia; which differ essentially from 
the genus to which they have been referred, in having 
ovaritum semisuperum and in the ripe fruit the pericar- 
pium almost entirely superior. With some unpublished 
species these form a very distinct genus which I have 
called Photinia. 
Our knowledge of European Roses has become, by 
the extraordinary attention they have received, so ex- 
tensive that it is impossible to doubt that limits be- 
tween what are called species do not exist. This was 
strongly suspected by Linnzeus when he said, “ Species 
limitibus difficillime circumscribuntur, et forte Natura 
non eos posuit,” but he had no means of satisfying 
himself. Gerard and others have asserted it; although 
Haller and most succeeding botanists have disputed the 
truth of the opinion. A partial, but satisfactory illus- 
tration of it may be given, without extending the exa- 
mination so far as to show every link which unites the 
European species with each other. R. canina and spi- 
nosissima may be considered to exhibit the extreme 
differences in structure and appearance. Let us begin 
with spinosissima. This is united with rubella through 
the variety melanocarpa of the latter. Its variety p7- 
losa connects it with R. involuta, which in a more vi- 
