ul] THE FERTILISATION OF FLOWERS. 45 
flowers, rotundifolia has small ones. In the former 
the stamens and stigmas are so arranged that self- 
fertilisation is impossible; in the latter they are so 
placed that self-fertilisation cannot be avoided. A 
similar instance occurs among the species of Willow- 
herbs (Efzlobium). 
Among the various species of Wild Geranium we 
have some with large flowers and some with small. 
Of the large-flowered species we 
will take Geranium pratense as the 
type. Its flowers are erect and 
opened wide by day; at night 
they hang down partially closed. 
When the flower first opens the 
pistil is immature. It is divided Fic. 52. 
into five stigmatic lobes, and when 
immature these lobes have the stigmatic surfaces in 
contact, as shown in fig. 51a. When the flower opens 
the ten stamens also are immature and lie flat on the 
petals. Five of them become matured and raise 
themselves parallel with the pistil, shed their pollen 
and retire to their former position, They are succeeded 
by the other five, and when these have retired the 
stigmas unfold as in fig. 514. From this it will be 
seen the flower cannot fertilise itself. But in the 
smaller species, of which the well-known Herb Robert 
(G. Robertianum) is an example, the stigmas are 
mature before all the pollen is shed, so that if cross- 
fertilisation does not take place self-fertilisation does. 
Here the size of the flowers is evidently due to the 
visits of insects, and no doubt Sir John Lubbock is 
right when he remarks: “It would seem that, as a 
