65 



Observations reveal the fact that cross-pollination is accomplished mainly by 

 two agencies, the wind and insects. Wind-pollinated flowers have dry, powdery 

 pollen, feathery stigmas (as a rule), inconspicuous, regular corollas, and no odor 

 or nectar. Insect-pollinated flowers, on the other hand, have sticky pollen, 

 showy, often bright colored and irregular corollas, nectar, and attractive odors. 



A close study of plants reveals the fact that a very large number are modified 

 in some form to secure cross-polhnation. The principal devices adopted are: 



(1) Diclinism^ or the separation of the stamens and pistils on different 

 flowers, on the same plant or on different platits; 



(2) Dichogaimy, the difference in time of maturity of stamens and pistil on 

 the same fl^ower; 



(3) Special contrivances in the flower whereby cross-pollination is favored; 

 and 



(4) Self-sterility, or the inability of a flower to set fruit with its own pollen. 



In the apple and^pear there is a slight difference in date of maturity of stamens 

 and pistil, the pistil maturing first. In the clovers, as we shall see, there is a 

 special structural contrivance which enables foreign pollen to reach the stigma 

 first. Besides, these blossoms contain abundant nectar. Self-steriUty is common 

 in orchard varieties, particularly of pears, plums, and grapes; and the list is fairly 

 large. This fact alone shows the important part played by cross-pollination. 



When, therefore, the flora of a country is closely studied it is found that 

 insect cross-pollinated flowers can be told, even at a glance, in many instances. 

 They always show the associated characters which I have already indicated, viz. : 

 colored corolla, sticky pollen not capable of being wind-blown, and the presence of 

 nectar and often of odors. Frequently, besides, they have some special device 

 which favors cross-poUination. 



Now, orchard blossoms and clover blossoms possess all the characteristics of 

 insect cross-pollinated flowers, and if it is found that bees are the main insect 

 visitors, the evidence is convincing that bees are the main agents in the production 

 of fruit and the setting of seed. 



The Apple Blossom. The flower of the apple is perfect, i.e., has both 

 stamens and pistil. The calyx is urn-shaped, upon Avhich rests the corolla with 

 five rose-colored petals. There are numerous erect stamens. At first they are 

 crowded together in the middle of the flower, and the unripe pollen sacs (anthers) 



P. P. Eng.— 5 



