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474
edly the somatic number in the race examined will be found to
be eighteen.
In the case of longiflora there is no such variation in chromosome
number in P. M. C. Ten chromosomes have uniformally been
counted in heterotypic metaphase, anaphase and in homotypic
anaphases. The situalion described above for alata suggests one
way, at least, in which a ten chromosomed form might have
arisen. Further study of other races of this species must, also,
be made. ;
A more detailed examination of suaveolens, originally stated pro-
bably to have twelve chromosomes, indicates that x —18 is the
correct number for this species. |
A number of varieties of Tabacum have been used in crosses
with sylvesiris and with other species, as follows.
Sylvestris X Tabacum vars. macrophylla, angustifolia, macrophylla
purpurea, "Maryland", *Cuba*.!
Tabacum X paniculata.
Tabacum X glutinosa.
It is the purpose of the present preliminary note to comment
upon the cytological phenomena exhibited by F, hybrids of syl-
vestris X Tabacum. Material of sylvestris X Tabacum vars. angusti-
folia, “Cuba“ and *Miradato^? has been examined; the most com-
plete series of stages being obtained in the cross with *Miradato*.
The somalic number in these hybrids is thirty-six and twelve
bivalent and twelve univalent chromosomes appear in heterotypic
metaphase in both P. M. C. and E. M. C. The distinction between
semini and single chromosomes is sharp as indicated in fig. 1
c and d.
In the first division of P. M. C. there are two successive stages,
one involving the separation of the partners of the bivalents and
the other the division of the univalents. In late metaphase the
bivalents are rather accurately disposed in the equatorial region,
some of the singles lying between them but, for the most part,
! For a taxonomic discussion of the species and varieties referred to, see
SETCHELL, Univ. Calif Publ Botany, vol. 5, no. 1, 1912.
* Material of var. “Miradato“ was kindly put at my disposal by Dr. W. BATESON,
and I am much indebted to Mr. Newron of the staff of the John Innes Horti-
cultural Institution for fixing material of this variety and of the cross with
sylvestris
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