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309
has been molher — the contrary is improbable — give a hybrid
that theoretically is most likely to get 14 + 28 = 42 chromosomes.
Further, if the 14 gallica-chromosomes conjugate with the same
number of chromosomes from the pentaploid rose, there theoreti-
cally will be found 14 bivalent and 14 univalent chromosomes in
the diakinesis stage of the hybrid. I found precisely this number
of gemini and singles in examining the common white rose, R.
alba L., which is generally granted to be a hybrid between gallica
and dumelorum, the latter being pentaploid. Not only this one but
also the other forms in my material determined as hybrids between
representatives of the seclion Caninae and roses of other sections
have possessed the theoretically expected chromosome combinations,
for instance hibernica (canina x pimpinellifolia), certain forms of
involula (tomentosa x pimpinellifolia), other forms of involuta (villosa x
pimpinellifolia), and canina x ’pendulina.
19. A cytological examination, therefore, can be of use when
the hybrid origin of such roses is to be controled. By this method
it is also possible in certain cases, to find out to which group of
species the parents of a hybrid belong (compare the involula-forms,
point 18).
20. Though the species of the section Caninae have preserved
the power of sexual reproduclion, manifested by the character of
the tetrad divisions in the ovules and the anthers, by experiments
(MarssoN) and the existence of numerous spontaneous hybrids,
they almost exclusively produce seeds in an apomictical way. This
kind of seed-formalion is experimentally proved by Marssow,
SCHWERTSCHLAGER, and others. The chromosome sets found are
a cytological proof. The mentioned combinations of bivalent and
univalent chromosomes in equal multiples of 7, stated in nearly
all my examined material of such roses, are namely not maintained
in bushes originated from seeds which are produced in a sexual
way. I have examined some spontaneous hybrids between forms
belonging to this section, and I found in them very diverging
chromosome sets, the sporophyte number being 32—36 and the
number of the bivalents rather variable (type 10, anorthoploid forms).
This chromosome condition is due to the mentioned disturbances
in the distribution of the unpaired chromosomes in course of the
reduction divisions.
21. From the preceding point follows, that a bush belonging
to the section Caninae and not having bivalent and single chro-
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