Peas and Clover 147 
mass pushes the lengthening pistil, and when a bee 
alights upon the wings and depresses them and the 
interlocked keel, the pollen is forced out on the bee’s 
under-side. On a second or third visitor arriving, the 
now mature stigma is pressed against a similar part, 
in all probability bearing pollen brought from 
younger flowers. The pistil and pollen Gf any left) 
fall back into their former position when the weight 
of the insect 1s removed. 
The Kidney Vetch (Anthyllis vulneraria) has 
similar mechanism for fertilisation, yet there are 
two or three interesting differences in the flower- 
parts. The calyx is inflated and tubular, and so to 
avoid a waste of material the petals all have long 
claws, but of course such an arrangement in a low- 
growing plant leaves the honey exposed to such small 
creeping insects as may effect an entrance to the 
calyx. To guard against such a danger, the calyx 
is covered with woolly down, and even the leaves 
are covered with silky hairs to discourage them at 
the outset. Another result of the tubular shape of 
the flower is that only long-tongued bees can reach 
the honey. 
The Rest-harrow (Ononis spinosa), though of similar 
structure, does not produce honey, therefore there is 
no free stamen, for there is no necessity for leaving 
an opening to the staminal tube. Yet the flower 
is fertilised by bees, and by bees only. It would 
appear that though they get no honey they have not 
yet learned to avoid so attractive a flower; there can 
be little doubt that in this case the rosy tint and 
large size of the flower lead them to expect more 
than they find. According to the observations of 
