116 THE FLOWERING PLANT. 
mate agent, and, for the same reason, both scent and nectar are 
wanting. Stamens and stigmas project well out of the flower 
when they are mature, so as to catch the wind. Pollen is pro- 
duced in very large quantities, as it is evident much must be 
wasted, while at the same time it is dry and powdery, its grains 
also being generally smooth. In firs and pines each pollen grain 
is provided with a pair of little air-bladders (fig. 45), which offer 
an increased surface. The stigmas, again, are remarkable for 
their size and the presence of numerous hairs or roughnesses. 
Frequently, too, they are branched, and, in short, are admirably 
adapted for catching pollen. It is also to be remarked that the 
flowers are mostly unisexual. Our native trees are for the most 
part wind-pollinated, and so inconspicuous are their flowers that 
many are popularly believed to have none at all. They usually 
flower in early spring, before the foliage leaves are unfolded, and 
this evidently has to do with the unimpeded dispersal of pollen. 
All catkin-bearing trees (except willow) may be cited as examples, 
the principal kinds being alder, birch, hornbeam, hazel, beech, 
oak, and poplar. These possess all the above-mentioned charac- 
teristics of wind-pollinated flowers. Poplar is dicecious, the others 
moncecious. 
Take, for instance, hazel, the flowers of which have already 
been described (p. 99). The male catkins are pendulous upon 
slender stalks, and the slightest breath of air can move them. 
Their character is well expressed by the popular name of “ lambs’- 
tails.” The group of pink threads projecting from the bud-like 
female catkins are the forked stigmas. 
The Scotch fir is another excellent example of wind-pollination. 
It is monecious, and the smallest female cones (cf. p. 99) are the 
ones ready for pollination, Vast quantities of pollen are pro- 
duced in June, and even a gentle breeze blows it away in yellow 
clouds. ‘The so-called ‘sulphur showers” of North America are 
of this nature, and they often form a scum on the surface of 
water miles distant from fir forests. Such a shower occurred in 
Inverness-shire in 1858, covering the ground to a depth of half 
an inch. More pollen is necessary in this case, since blooming 
takes place when abundance of foliage is about, although the 
evergreen needle-like leaves of the fir do not block up the flowers, 
as broader ones would do. Between the scales of the female 
cones ready for pollination a viscid substance is excreted. This 
catches pollen grains, and then gradually dries up, drawing them 
down to the micropyles as it does so. 
Willow and lime, although their flowers possess no scent, 
and an inconspicuous perianth respectively, are both insect-polli- 
nated. The former is dicecious (cf p. 99), and every male and 
