FLOWERS AND THiail WORK 



47 



of the pollen grains never reach their destination and are 

 W!ist(>(l. Therefore in such plants sen- oral thousands, perhaps 

 hundreds of thousands, of pollen grains will be developed to every 

 ovule produced. Such arc the i)incs. In May and early June 

 the ground under pine trees is often >ellow with pollen, and the 

 air nia>' be filled with tlu' dust for miles from the trees. Such, 

 also, is the case with many of the grasses. 



(2) The anthers are usually exposed to the wind when ripe. 

 The common plantain and timothy grass are excellent examples. 



(3) The pistil of the flower is peculiarly fitted to retain the pollen 

 by having featliery projections along the sides which increase the 

 stigmatic surface. This can be seen in the grass. In the Indian 

 corn the stigmatic surface is the so-called silk which protrudes 

 beyond the covering of modified leaves which form the husk of the 

 ear of corn. All our grains, wheat, rye, oats, and others, have the 

 t\pical feathery pistil of the wild grasses from which they descended. 



(4) The corolla is often entirely lacking. It would only be in the 

 M'a.\' in flowers that are dependent upon the wind to carry pollen. 



Imperfect Flowers. — Some flowers, the wind-pollinated ones 

 in particular, are imperfect ; that is, they lack either stamens or 

 pistils. In such flowers, cross-polh- 

 nation must of necessity follow. 



If only the starainate flowers (those 

 which contain only stamens) arc developed 

 on one plant, and only the pistillate (those 

 which bear only pistils) on another, \\ c call 

 the plant dioecious. A common example is 

 the willow. 



Other plants bear staminato and pistU- 

 lato flowers on the same plant. In this 

 case they are said to lie monacious. The 

 oak, hickory, beech, birch, walnut, and 

 chestnut are familiar examples. 



The pine tree is another example of monoecious tree ; the male or 

 staminate flowers appear in tiny clusters called catkins, the female or 

 pistillate flowers coming a little later as tiny cones, which in most species 

 of pines take nearly- two years to produce seeds. 



Water Pollination. — An unusual method of pollination is found 

 in those plants which live almost entirely under the water. In eelgrass 

 the pistillate flowers are attached to long, slender stalks and float on the 



Imperfect flowers of the squash, 

 the corolla removed. Pistil- 

 late flower at the left. 



