Gates .— The Chromosomes of a Triploid Oenothera Hybrid. 569 
Thus pollen grains will be formed having every chromosome number 
between 11 or 12 and 7. As pairs of tetrad nuclei usually have the same 
chromosome number, aberrant forms should be looked for in pairs in the 
next generation. 
These experiments were aided by grants from the Royal Society and 
the British Association. 
Literature cited. 
Gates, R. Ruggles ( 1909 ) : The Behaviour of the Chromosomes in Oenothera latax gigas. Bot. 
Gaz., xlviii. 179-99, Pis- 12-14. 
-( 1913 ) : Tetraploid Mutants and Chromosome Mechanisms. Biol. Centralb., 
xxxiii. 92-9, 113-50, Fig. 7. 
- ( 1915 ) : The Mutation Factor in Evolution, with Particular Reference to Oeno¬ 
thera. London, Macmillan, pp. 353, Figs. 114. 
van Overeem, Caspar ( 1920 ) : liber Formen mit abweichender Chromosomenzahl bei Oeno¬ 
thera. Dissertation. Beihefte z. Bot. Centralblatt, xxxviii, pp. 47, Pis. 6. 
- ( 1922 ): Same title. Ibid., xxxix, pp. 1— 8o, Pis. 15. 
EXPLANATION OF PLATE XII. 
Illustrating Professor Gates’s paper on the Chromosomes of a Triploid Oenothera Hybrid. 
All figures were drawn with a -j— in. Koristka immersion lens N A. 1*30 and compensating 
ocular 12, tube length 152 mm., and reduced one-fourth in reproduction, giving a magnification of 
2,250 diameters. 
Fig. 1. Heterotypic anaphase in a pollen mother-cell of Oe. rubricalyx x gtgas, showing 
twenty-one chromosomes somewhat scattered. 
Fig. 2. Homotypic metaphase, showing ten chromosomes on right-hand spindle and probably 
eleven on left-hand. 
Fig. 3. Homotypic anaphase, showing ten split chromosomes separating on right-hand spindle 
and nine on left-hand. The other two chromosomes were evidently lost on the heterotypic spindle. 
Fig. 4. Homotypic anaphase, showing the two daughter groups of eight chromosomes on the 
left-hand spindle and two groups of seven on the right-hand. The remaining six chromosomes must 
have been lost in the heterotypic mitosis. 
Fig. 5. Homotypic telophase, showing seven chromosomes entering each daughter nucleus, and 
an eighth divided but left behind. 
Fig. 6. Homotypic telophase, showing eight chromosomes at either end of spindle and a ninth 
split chromosome disintegrating on the spindle. 
Fig. 7. Homotypic telophase, showing seven chromosomes at each pole of the spindle, the 
eighth divided but left behind. 
