220 
F. W. Oliver. 
corolla of the ray florets begins to curl up like a watch spring and 
when about half the corolla is twisted all the ray florets bend over 
and cover the disc, thus initiating the fruiting stage of the capitulum. 
While the disc florets are active the ray florets close up every 
night, producing the well-known nocturnal condition of the 
capitulum but with no curling of the tip of the corolla. 
In Avctotis aspera Linn. (syn. A. aureola) we have the following 
noteworthy points. (1) Three types of florets—female, hermaphro¬ 
dite and male. (2) Irritable styles in the disc florets. (3) Diurnal 
exsertion and retraction of the styles of the disc florets. (4) Diurnal 
progression of maturity towards the centre of the disc. (5) Perma¬ 
nent withdrawal of the style of the inner florets after the work of 
pollen presentation is completed. (6) Nocturnal closing of the 
capitulum by the ray florets. 
As material and opportunities for constant observation were 
not available I hope to make more detailed observations when 
military exigencies permit. In conclusion I would express my 
thanks to Mr. R. Irwyn Lynch, M.A., for material and for the 
opportunities given for the study of this interesting member of the 
Compositae during the time I was recovering from a shrapnel wound 
in a Cambridge hospital. 
FOREIGN POLLEN IN FOSSIL SEEDS. 
By F. W. Oliver. 
HE appearance of Mr. Birbal Sahni’s short but interesting 
paper on Foreign Pollen 1 tempts one to contribute a brief note 
on the same subject. Mr. Sahni records the fact that of the ovules 
of Ginkgo investigated, about a dozen in all, no less than eight 
contained foreign pollen grains. Among these, three distinct species 
of grains were discriminated, whilst in at least one instance a pollen 
grain of foreign origin was found to have germinated, producing a 
tube. 
As the author justly remarks, the conditions which prevail in 
botanic gardens and similar artificial habitats are particularly 
favourable to occurrences of the kind. Provided the liberation of 
wind-borne pollen synchronises with the presence of collecting 
drops at the micropyle there is no obvious reason why the pollen 
grains should not find their way to the pollen chamber—so long of 
course as they conform in the matter of size. 
1 New Phytologist, Vol. XIV, 1915, p. 149. 
