Hybridism and Classification in the Genus Rosa. 161 
a few notes on the arrangement may be useful. The group 
canina includes that large assemblage of forms characterised 
by the possession of glabrous leaflets, glabrous or slightly hispid 
styles, late-ripening fruit and reflexed sepals which disarticulate 
before the fruit changes colour. The group dumetorum 
is the exact counterpart of canina except that its leaflets are 
more or less pubescent. Its numerous forms may be grouped 
together as an aggregate species, R. dumetorum Thuill. or they may 
be regarded simply as hairy-leaved varieties of R. canina. 
R. glauca Vill. and R. coriifolia Fr. are distinct and clearly 
defined from R. canina and R. dumetorum. Their members 
develop ascending or erect sepals which are subpersistent, 
not falling until the ripening of the fruit. Moreover, the fruit 
ripens earlier than in canina or in dumetorum. The styles, 
which are never much exserted, form a dense hemispherical mass, 
strongly hispid or woolly, a character by which it is nearly always 
possible to distinguish members of R. glauca and R. coriifolia from 
those of R. canina and R. dumetorum. R. glauca comprises 
glabrous forms; in R. coriifolia the leaflets are hairy. I regard 
the four groups as constituting two sets of parallel series of forms. 
The first two are generally distributed throughout Britain while 
the third and fourth are confined to the north of England and to 
Scotland. 
The four groups have been fairly fully worked out systematically 
and a lai ge number of forms have been described and named. No 
attempt will be made to give an exhaustive analysis of all these 
forms based on many characters, but in Table II the primary 
divisions of the groups are shown and it will be seen that the 
characters used are the serration of the leaflets, the presence or 
absence of subfoliar glands, the development or non-development 
of hispid peduncles. To these must be added, of course, the 
pubescence of the leaves as the distinguishing feature of R. 
dumetorum and R. coriifolia from R. canina and R. glauca 
respectively. The primary divisions of the four groups have been 
named in the table as if they corresponded to species, and while 
this is true for some, it has to be mentioned that others were 
described by their authors as varieties only. It is clear, however, 
that if the four groups are treated as equal in value, all the names 
which correspond to parallel divisions of the groups should also 
rank equally ; whether we call them species or varieties is a matter 
of individual opinion. 
