FLOWER AND FRUIT 165 
stigma is ready to receive it, as is the case with the 
Canterbury bell and daisy families, the flower is said 
to be protandrous. The little blue bell (Wahlenbergia), 
so common in wild places throughout New Zealand, is 
of this type. It may, however, be mentioned that, in 
both these familes, if cross-pollination fails,  self- 
pollination is effected by the coiling of the split style 
in such a way as to bring the stigma into contact with 
the pollen that clings to its outer surface. Where the 
stigma ripens first, as in the plantain and arum, the 
flower is protogynous. 
The third means by which self-pollination may be 
prevented is the arrangement of stamens and pistil 
in such a way that pollen from the former cannot reach 
the stigma. In such eases there is, of necessity, a special 
mechanism or arrangement, whereby cross-pollination 
by external agency is facilitated. So far, the discus- 
sion has dealt almost exclusively with the prevention 
of self-pollination. It will now be necessary to show 
by what means cross-pollination is effected. 
Wind is one of the great carriers of pollen, as 1s 
well seen in all pines and grasses. These produce great 
quantities of dry dust-like pollen, which, at certain 
seasons, fills the air, in the latter case to such an extent 
as to give rise to the complaint known as hay fever. 
Flowers that are wind-pollinated are usually small and 
inconspicuous, have long feathery stigmas and long 
stamens hanging well out of the corolla, as a rule are 
without perfume, and do not secrete nectar. These 
characteristics might be expected. They eliminate the 
useless expenditure of energy on the unnecessary 
attraction of insects, but are well adapted for the 
receiving and dispersal of pollen. The coprosma and 
piri-piri (bidi-bidi) are among the commonest and most 
typical of the native wind-pollinated plants. 
Insects are the chief agents of cross-pollination. 
Among the myriad mechanisms for preventing self and 
