SELF-POLLINATION 53 
Thus we learn that the devices in the vegetable 
world for preventing or delaying self-pollination come 
under four heads: the stamens and pistil may be on 
separate plants, or in separate flowers on the same 
plant ; again, where they are both found in the same 
flower the separation may be either in time or in 
space, or, indeed, in both. 
(d) Self-pollination 
Before I finish with Pollination, however, I must 
say a little about the devices for effecting self-pollina- 
tion, in the event of a cross having been missed ;_ but 
they are so many and so varied that I can only refer 
to a very few of the commonest of our wild or garden 
plants. 
We have just learnt that where it is not an absolute 
impossibility self-pollination is hindered by the 
separation of the grains and the stigmas, and we must 
now see how the hindrance is removed. The Butter- 
cup is a plant which ripens its stigmas first and its 
grains afterwards ; but there are quantities of others 
in which the grains are the first to mature, and the 
Ragged Robin is a good example. 
If we watch a blossom of either of these plants 
we shall see that there are two well-marked stages, in 
the first only one of the two actors comes into play; but 
the point is that, in each case, that one still goes on 
playing its part after the other has matured. In the 
first stage, therefore, cross-pollination is the only 
possibility ; but in the second there are good chances of 
self-pollination too. 
It may, however, occur to the reader that, although 
the separation in time has come to an end, the grains 
and the stigmas are still separated in space, and this 
