164 Blackburn and Harrison . — The Status of the British 
folia and a member of the Villosae, using the sectional name in its widest 
sense as covering the Rosa mollis , R. omissa , R. tomentosa , and R.foetida 
groups. 
After careful study in the field of the bush whence our preparations 
were derived, and making due allowance for its neighbours, we have decided 
that its exact parentage is R. pimpinellifolia x R, sy Ives iris — seemingly 
quite a frequent combination in our two counties ; as confirmatory proof of 
its hybrid nature, if any were needed, we may say that, wherever we have 
come into contact with it, it has been uniformly barren — a point neglected 
by most previous writers, who have merely observed its wealth of blossom 
in June and July. 
Recognizing the importance of determining the somatic chromosome 
number correctly in order to procure confirmation of our diagnosis of the 
parentage, careful counts were made from clear prophases in the styles 
where, as is general in the genus, such figures are very frequent. Such 
counts prove difficult to make accurately, owing to the unusually large 
number of chromosomes present and their elongated shape. Nevertheless, 
in favourable nuclei, the number has been ascertained with complete 
exactitude to be 42 (Text-fig. 2, a). The precise significance of this number 
will be considered later. 
Coming now to the behaviour of the chromosomes during meiosis, 
unlike what we have noted in moth hybrids of the genus Lycia , the stages 
leading from the reticulum onward through synapsis seem absolutely 
normal. PI. X, Fig. 2 6, showing the synaptic knot at its greatest contraction, 
differs in no wise from the same stage depicted for Rosa arvensis on PI. IX, 
Fig. 2, and is quite representative of the number examined. By degrees 
the open spireme stage is attained in which the thread, in spite of its 
delicacy, can be followed in its continuity with sonde amount of ease as it 
winds around the periphery and elsewhere in the nucleus (see PI. X, Fig. 27). 
With the passing of this stage, certain of its threads are seen to lie parallel, 
thus initiating the formation of the bivalents. Here we must remark that 
it would appear a fair deduction, when one allows for the future development 
of bivalents and univalents pari passu , to assert that the chromatic thread 
as it emerges from synapsis is still univalent ; one cannot conceive of its 
being univalent and bivalent at one and the same time. This should be 
set against the parasyndetic appearance of the stage of R. pimpinellifolia 
depicted on PI. IX, Figs. 5-7, as it seems unlikely that the species should 
differ in this respect. 
Gradually the chromosomes thicken and concentrate, and very early 
indeed it becomes evident that whilst certain individuals are, without any 
possible doubt, bivalent, others just as assuredly remain unpaired and can 
often enough be detected as marvellously straight single rods. Con- 
centration proceeds regularly in bivaknt and. univalent alike until in 
