I 1 6 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 dioecious, the others 

 monoecious. 



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 monoecious, 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 dioecious (cf. p. 99), and every male and 



