The Chromosomes of a Triploid Oenothera 
Hybrid. 
BY 
R. RUGGLES GATES, Ph.D., F.L.S., 
Professor of Botany , University of London ( King's College). 
With Plate XII. 
I N 1912 crosses were made at the John Innes Horticultural Institution 
between Oenothera rubricalyx and Oe.gigas. The Oe. rubricalyx parent, 
having 14 chromosomes, was descended in the third generation from the 
original mutant which occurred in 1907. The Oe.gigas parent belonged to 
the second generation from seeds obtained from the Palermo Botanical Garden 
under the name of Oe. cognata. This race was identical in character, 
chromosome number ( 28 ), and variability with the gigas mutant of de Vries’s 
cultures, and it doubtless represented an independent origin of the tetraploid 
condition. A further account of this race was published elsewhere (Gates, 
1913 ). 
P'rom the cross Oe. rubricalyx x gigas 199 seeds were obtained in one 
capsule. They were sown in 1913 at Rothamsted, but only one plant 
developed. The rosette leaves were large, broad, and crinkled like those of 
gigas , and the midribs were green below, not red as in rubricalyx. The 
plant grew very large, stout and taller than the parent forms, as is usual in 
triploid hybrids. The leaves stood out from the stem and the flowers were 
‘ very large ’, the buds showing the red sepals and hypanthium of rubri¬ 
calyx , but conspicuously pale in colour. The leaves were less crinkled than in 
gigas. Thus in this hybrid with 2 x chromosomes from the male paventgtgas 
and x from the female parent rubricalyx , the usually dominant red pig¬ 
mentation character was so diluted as to be invisible on the rosette leaves 
and pale on the buds. The foliage was intermediate, but more like that of 
gigas. Examination of the pollen showed that f bad ’ grains and ‘ good ’ 
grains were in the ratio of about 4: 1. The apparently functional grains 
were four-lobed (as in gigas) or three-lobed in the ratio of about 2:1. 
The lobing of Oenothera pollen grains has been discussed elsewhere (Gates, 
[Annals of Botany, Vol. XXXVII. No. CXLV 1 II. October, 1923.] 
