Gee THE AUSTRALIAN NATURALIST. 
fertilised by pollen from another individual; and that if 
a flower be pollinated by itself, it is disadvantageous to 
the individuals produced from the resulting seed. Still, 
there are some flowers which are regularly fertilised by 
their own pollen, or, as it is technically termed, self-pol- 
linated. 
To any one examining an ordinary flower, it would 
seem as if self-pollination must be the rule, as the anthers 
are so close to the stigma that the pollen must reach that 
organ. But Nature gets over this difficulty in several 
simple ways. ; 
The anthers mature first and drop the pollen out, 
but the stigma is not then in a fit state to receive it, and 
the pollen drops off, or is blown or taken away. Then 
the stigma matures, and is ready to receive pollen. Of 
course there is always a chance of the flower’s own pollen 
remaining on the stigma, but again Nature provides a 
remedy. She makes the pollen from distinct individuals 
prepotent over the flower’s own pollen, and this is carried 
_so far that in some cases the flower’s own pollen, as Darwin 
showed, is actually injurious to the stigma, sometimes even 
causing its death. Plants whose pollen ripens before the 
stigma is mature are said to be protandrous, and this is 
the commmonest method of preventing self-pollination. 
In other plants the stigma becomes fit to receive 
pollen before the anthers dehisce; this is termed pro- 
togyny. 
A third method is the separation of the pollen, and 
ovule-bearing flowers; either they are on separate parts 
of the plant or they are on different plants. : 
These three states of the flower, then, are the fac- 
tors which make cross-fertilisation the rule amongst the 
‘flowering plants. 
Since plants can rarely be fertilised by: their own 
pollen, we have next to consider what provision is made 
to convey pollen from others flowers at the proper time. 
Some agents are necessary for this, and they are, Ist, 
wind; 2nd, water; 3rd, living organisms. Among our 
native plants, Casuarina is a good example of wind pol- 
lination. The flowers of wind-pollinated plants are’ usu- 
ally inconspicuous; their stamens are usually on very 
long and slender filaments, so that they are easily shaken 
by the wind. They produce large quantities of small 
