66 



are on the same level as, or a little below, the five stigmas which mature earlier. 

 Anthesis (opening of the sacs) begins about two days after the opening of the 

 buds, and lasts from five to six days. The outer anthers open before the inner. 

 Self-pollination may occur in those varieties where the stamens keep opening for 

 some time, and at the fading of the flower when the styles bend outward among the 

 stamens. 



Pear Blossoms. The petals are white and attractive as in the apple. 

 Anthesis lasts from seven to eight days. On the opening of the flowers the central 

 stigmas are already mature, and the styles stand erect and above the unripe stamens 

 which bend inward and guard the passage to the nectar. As a result, the insect 

 ahghts on the stigma and effects cross-pollination. This protogynous stage lasts 

 from two to four days. 



It will be seen, therefore, that cross-pollination is absolutely essential. 

 Although some varieties are fertile with their own pollen, yet many require to be 

 pollinated by another variety. Nectar is secreted copiously in the cup-shaped 

 disk, which attracts bees and other insects. Pollen is transported from tree to 

 tree by bees and other insects, and not by the wind. 



Red Clover Blossor&i. The blossoms of Red Clover are irregular and aggre- 

 gated into spherical heads. The corolla is composed of five petals united at the 

 base, an upper large petal (the standard), two side petals (the wings), and two 

 lower petals united in a keel-shaped structure (the keel). The " keel " contains 

 the ten stamens with nine filaments united to form a tube, and the pistil with a 

 long style. The stigma projects above the anthers to some extent. The nectar 

 is found at the base of the stamen tube at their junction with the claws of the 

 petals. 



When a bumble bee lights on a blossom its weight depresses the interlocked 

 wings and keel, and causes the stigmas and anthers to protrude beyond the apex 

 of the keel and strike the under surface of its body which is covered with pollen 

 brought from another flower. On account of the greater length of the style, the 

 stigma strikes the body of the bee before the anthers do, thus effecting cross-poll- 

 ination. Self-pollination, it is true, must often occur, but it is ineffective, as 

 shown by Darwin and others. 



To reach the nectar, insect visitors must have a beak 9-10 mm. long, but 

 " any insect sufficiently heavy to press down the keel can pollinate the flower." 

 The bum.ble bees have long beaks and are able to get the nectar and at the same 

 time pollinate the stigmas. 



White Clover. The flowers are white or reddish, and have a sweet smell. 

 The stigma projects beyond the anthers and bees alone are able to work the 



