Cytological Studies on Oenothera. I. 
Pollen Development of Oenothera grandiflora. 
BY 
BRADLEY MOORE DAVIS. 
With Plates XLI and XLII. 
^ 1 "'HE interest which attaches to the Oenotheras on account of their 
JL intimate relation to the mutation theory of De Vries has already led 
to their cytological study by three investigators. These authors have, 
however, approached the problems either through Oenothera Lamar ckiana 
itself or through some of its derivatives. They have consequently dealt not 
with old or well-established wild species, but with forms of recent or uncertain 
origin, for the relation of Oenothera Lamar ckiana to the American flora 
is certainly problematical. The present study will treat of a characteristic 
native species which is perhaps as true to its type as any American form. 
Further investigation may show that there are certain advantages in 
approaching the cytological study of the Oenotheras through species of 
established position. 
Oenothera grandiflora , Ait., is probably one of the most favour- 
able of the American types for cytological research on the pollen mother- 
cells, since the remarkably large and showy flowers have anthers which are 
about twice the size of those of O. biennis and almost as large and robust as 
the anthers of O. gigas . The plants which furnished the material for this 
investigation were grown from seed collected by S. M. Tracy at Dixie 
Landing, near Tensaw, Alabama, September 3, 1907. The seedlings were 
started during the winter in the hot-houses of the Harvard botanic garden 
and planted at Woods Hole, Massachusetts, in the spring of 1908. They 
developed during the summer into sturdy plants more than two metres 
high, which flowered profusely in September. 
I am greatly indebted to the Bureau of Fisheries for the hospitality of 
its laboratory at Woods Hole during several months, and to Miss Sarah B. 
Fay for garden facilities. 
Methods. 
It is difficult to fix the anthers of Oenothera satisfactorily, and great 
care and patience are necessary in such a manipulation as will assist 
the killing fluid to wet quickly the surface of the anther, otherwise the 
[Annals of Botany, Vol. XXIII. No. XCII. October, 1909.] 
