Cytological Studies on Oenothera. II. 
The Reduction Divisions of Oenothera biennis . 1 
BY 
BRADLEY MOORE DAVIS. 
With Plates LII and LIII. 
T HE following account of the reduction divisions of Oenothera biennis , L., 
is presented as a part of the writer’s plan to study certain characteristic 
native species of Oenothera as a basis for comparison with O. Lamarckiana 
and some of its derivatives, and as preliminary to the investigation of certain 
hybrids which may readily be obtained. The first paper of this series, 
‘ Pollen Development of Oenothera grandijlor a ’ (Davis ’ 09 ), gives an account 
of the reduction divisions in the pollen mother-cells of one of the larger 
American species, which exhibits some interesting peculiarities that are 
more easily understood after comparison with the conditions in O. biennis. 
Both of these American wild species give opportunity for a comparison of 
the reduction processes with those of O. Lamar ckiana and O. rubrinervis 
studied by Geerts and Gates. 
As is well known, Oenothera biennis is a species which exhibits a 
considerable range of variation in the size of its flowers, character of its 
foliage, and habit of growth, so that it is frequently possible to distinguish 
forms from different regions of America, and it is probable that races or 
strains may be readily differentiated by pure cultures. The fact that the 
flowers are self-pollinated before the opening of the bud would undoubtedly 
greatly assist in holding any differentiated races reasonably true to their 
types. The strain which furnished the material for this investigation was 
derived from a rosette transplanted from waste ground at Woods Hole to 
the author’s garden, in 1908. The rosette was selected with some care as 
an interesting type to hybridize with O. grandiflora with certain ends in view. 
The cross was made during that season and some of the hybrids of the first 
generation have been briefly described in a paper,‘Notes on the Behavior 
of Certain Hybrids of Oenothera in the First Generation ’ (Amer. Nat., 
vol. xliv, p. 108, 1910). 
1 An investigation conducted with aid from the Elizabeth Thompson Science Fund, for which 
the author desires to express his indebtedness. 
[Annals of Botany, Vol. XXIV. No. XC VI. October, 1910.] 
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