376 THE BIOLOGY OF FLOWERING PLANTS 



brilliantly coloured floral envelopes. This may be related 

 to wind pollination in two ways. It may be regarded as 

 a loss of characters which have become unnecessary 

 and therefore wasteful. It also favours wind pollination 

 positively by getting rid of organs which impede the free 

 scattering of the pollen from the stamens, and its easy access 

 to the stigmas. Many anemophilous plants have certainly 

 been derived recently, in the evolutionary sense, from insect- 

 pollinated ancestors. Thalictrum, the wind-pollinated 

 meadow rue, is an example. Though belonging to a family 

 remarkable for brilliant flowers and advanced specialisation 

 for insect visits, it possesses no corolla. We cannot be sure 

 that in all cases wind-pollinated plants have had entomo- 

 philous ancestors. The angiosperms may be polyphyletic in 

 origin, and it may well be that such families as the Gramineae 

 and Cupuliferae have never, in the course of their descent, 

 passed through a gaily flowered entomophilous stage. Wind 

 pollination in the gymnosperms is certainly primitive. 



On the positive side we find peculiarities in the structure 

 of the stamens, stigmas, and pollen grains. These last are 

 generally small in size, quite smooth in surface, and produced 

 in enormous quantities. Near pine woods sheets of water 

 may be covered with a yellow sulphur-like dust when the 

 microsporangia dehisce in spring. Any one who has 

 brought a spray of hazel catkins or of elm or ash blossom 

 into the house knows how thick the dust of pollen settles 

 on the table where it stands. Compare this with the be- 

 haviour of another plant in which the pollen is also abundant 

 and conspicuous. The scarlet Lilium bulbifenim has 

 brilliant orange- scarlet pollen, and the large anthers brim 

 over when they dehisce, but the grains stick about the 

 anthers or fall in lumps on to the petals. They are not 

 emptied in the air even when the flower is shaken. This 

 is characteristic of the insect-visited plant. In the wind- 

 pollinated plant the separation of the grains, the absence 

 of any tendency to stick together, due to the absence of 

 sculpturing, is most important, for, along with small size, 

 it increases the time during which the grains will float, like 



