THE NATURE-STUDY OF PLANTS 
Or 
Ww 
Now, I do not think it would require much argu- 
ment to persuade us that both the wind and the 
insects effect cross-pollination; but, on the other hand, 
it is quite certain that with the plants, whose flowers 
bear stamens and pistil in one and the same blossom, 
the insects at any rate might be responsible for a 
good deal of self-pollination as well, and we should, 
therefore, in view of the greater value of a cross, be 
on the look-out for any arrangement calculated to 
prevent the former, at least until there has been 
time enough to afford opportunities for a cross; for 
if that does not take place—if, for example, a flower is 
not visited by the insects—self-pollination is preferable 
to none at all. 
The two chief ways in which it is hindered until it 
becomes desirable are by separating the stamens from 
the stigma, either in time or else in space. 
A good example of the former is afforded by the 
Foxglove, and also by our Christmas Roses and 
Columbines. In the first the anthers open before the 
stigmas mature, so that there is a good chance of the 
pollen grains of any given flower being carried off by 
Bumble Bees before its stigmas are ready to be 
pollinated. In the other two, it is the stigmas that 
mature first, and an insect which visits either of them 
when the blossom is freshly opened must pollinate it, 
if at all, with grains from another blossom. 
Separation in space occurs as commonly as separa- 
tion in time. If we examine a Tulip we shall see that 
the stamens and the pistil are so far apart that there 
is not much chance of the pollen grains getting on to 
the stigma, especially as the insect visitor intrudes his 
person between the two, and so will touch each with 
the opposite side of his body. 
