The Status of the British Rose Forms as determined 
by their Cytological Behaviour. 
BY 
KATHLEEN B. BLACKBURN, M.Sc., 
AND 
J. W. HESLOP HARRISON, D.Sc., 
Armstrong College , Newcastle-on- Tyne. 
With Plates IX and X, and five Figures in the Text. 
I. Introductory. 
T HE study of the genus Rosa was commenced in the year 1913, chiefly 
with the object of throwing, if possible, some light on one of the most 
baffling problems presented by the British Flora, that is, the value to be 
assigned to the various rose forms. This investigation was carried out at 
first simply from the systematic side, but so hopeless was the task rendered 
by the extraordinary polymorphism of the plants considered, that quite 
early it became evident that no real scientific progress could be expected 
from that standpoint alone. Nevertheless, that very variability provided 
the clue which we consider destined to establish the true status of the 
Rosae. 
Accustomed as we had been to work with hybrids (both plant and 
animal) of every degree of complexity, we could not help being impressed 
by the close analogy between the so-called rose species and our artificial 
hybrid products. The problem, therefore, shifted from the ground of the 
systematist to that of the geneticist, and we set ourselves to determine, if 
possible, the hybrid nature, or otherwise, of the plants we were studying. 
Two lines of approach seemed capable of yielding the desired solution : — 
1. Known hybrids like Rosenberg’s Drosera longifolia x D. rotundifolia 
amongst plants, and our hybrid Bistons and Oporabias amongst animals, 
when examined cytologically, display characteristic anomalies in their 
maturation divisions ; do the Rosae exhibit the same behaviour ? 
[Annals of Botany, Vol. XXXV. No. CXXXVI 1 I. April, 1921.] 
