Rose Forms as' determined by their Cytological Behaviour. 173 
just referred, and likewise keep the hairy-leaved forms separated from their 
glabrous allies. 
(1) Rosa canina , Linn. 
The segregates brought under examination were R. flexibilis, Deseg., 
R. fallens , Deseg., R. separabilis , Deseg., and R. parisiensis, Rouy, the first 
three forms being uniserrate and the other biserrate. 
Without exception all possessed a chromosome count of thirty-five in 
the nuclei of the somatic cells (Text-fig. 3, c, from R. lute liana) and were 
therefore pentaploid. 
As with R. coriifolia , these chromosomes were of two t^pes, as 
revealed during meiosis, fourteen being bivalents and twenty-one univalents 
(see PL X, Fig. 28). Text-fig. 3, i, represents a heterotype plate from the 
pollen mother-cell of R. parisiensis , and, as in R. coriifolia , the bivalents 
are arranged centrally with the univalents round them. Whilst generally 
the phenomena displayed during the stages immediately preceding the 
heterotype division and the distribution of the chromosomes during the 
division itself very closely resemble that visible in R. coriifolia (and 
therefore not requiring a full description), there is a more emphatic 
raggedness on both heterotype and homotype spindles, with regard to the 
univalents. This involves a greater abundance of micronuclei in the 
interkinesis between the maturation divisions, and a consequent accentuation 
of this number in the subsequent ‘ octad ’. 
However, as the seven chromosomes of the ‘ cap ’ seem never to be 
affected, this would appear, in some way, to be an advantage, for the 
functional pollen grains are bound to be much more generally endowed 
with that chromosome combination. In these plants, up to 50 per cent, 
of good pollen in the anther is not an unusual occurrence (see PL X, Fig. 44). 
This, in its turn, explains why, compared with the Afzelianae, the Eucaninae 
are more often fertilized and less prone therefore to apomixis. 
(2) Rosa dumetorum , Thuill. 
Rosa urbica , Lem., a uniserrate form, and R. hemiiricha , Rip., a biserrate 
rose, yielded our material. Both mierogenes are pentaploid. Once more 
the complement of thirty-five comprises fourteen destined to play the part 
df bivalents in the reduction division and twenty-one that of univalents, as 
the heterotype plate on Text-fig. 3, h, will show for R. urbica. 
In every detail the description of events given for the canina and 
coriifolia segregates, with the qualifications mentioned under the former, 
apply here ; to repeat them would thus be superfluous. Still, one fact 
should be noted ; in the hemiiricha form a much greater tendency seems 
to be manifested for the micronuclei to collaborate with their bigger 
companions in the development of the tetrad, so that multinucleate 
microspores are not uncommon. Also, necessarily, the concomitant of this 
