566 Gates. — The Chromosomes oj a Triploid Oenothera Hybrid. 
I 9 I 5 > P« 212 )> an d it was shown that grains with less than the full diploid 
number of chromosomes may still be four-lobed. Probably in this plant 
the four-lobed grains, which numbered about 12 per cent, of all the pollen 
grains, had not less than 10 chromosomes. Further reference will be made 
to this point later. 
At the end of the season this plant was potted and placed in a green¬ 
house. Its main stem died and was cut down. Then a number of short 
side shoots developed from the base bearing rosette leaves. These rosettes 
were mostly Wkegigas with broad-pointed crinkled leaves. One shoot, how¬ 
ever, was quite different, nearer Lamarckiana , with leaves pointed and 
nearly smooth. Another shoot was intermediate in character between these. 
Unfortunately no photograph was obtained, and although cuttings were 
attempted the plant finally died and was lost. The variation in the charac¬ 
ter of the leaves on different shoots was no doubt due to the loss of certain 
chromosomes from their growing points. This undoubtedly occurs, as in 
the meiotic divisions, through the dropping out of certain chromosomes in 
the cytoplasm, a process which may be expected to take place when a plant 
with an unbalanced chromosome number is placed in unusual conditions. 
Cytological material was collected in 1913 for a study of the meiotic 
divisions in this plant, but the embedded paraffin material was laid aside 
and was only sectioned last year. I am indebted to Miss E. M. Rees, B.Sc., 
for making the preparations (stained in iron-haematoxylin), and to Mrs. N. 
Ferguson, B.Sc., for the careful drawings. Fig. 1, PI. XII, is a side view 
of the heterotypic spindle in the pollen mother-cell. It shows 21 chromosomes 
somewhat scattered along the spindle, as is usual in many Oenotheras. The 
other illustrations have been selected to show how the 21 chromosomes are 
distributed in the reduction divisions and how the number gradually drops 
down, through the omission of chromosomes from the daughter nuclei in 
both divisions, until many of the pollen nuclei receive only 7. 
Fig. 2 is a homotypic metaphase showing 10 chromosomes in the right- 
hand group and probably 11 in the other. Usually this is the segregation 
which takes place on the heterotypic spindle, 10 chromosomes entering one 
daughter nucleus and 11 the other. Chromosomes may however be left behind 
on the heterotypic spindle. Thus in Fig. 3 we have a homotypic anaphase 
with ]8 chromosomes on the left-hand spindle and 20 on the right. Under 
the microscope these are clearly in two separate groups of 9 and 10 respec¬ 
tively, although the groups necessarily overlap somewhat in the drawing, 
since the spindles were obliquely placed. Hence 9 split chromosomes have 
separated normally on the left-hand spindle and 10 on the right. This 
means that a total of 19 chromosomes only is now present, and hence the 
other two must have been left behind on the heterotypic spindle and dis¬ 
integrated. Similar conditions have been observed in other pollen mother- 
cells. 
