THE FLOWER 239 



gamic. They are much more prolific than ordinary flowers, 

 but are not common, and seem to be a provision against 

 accident, for the plants producing them are generally pro- 

 vided with other flowers of the usual kind, some, as the 

 violet, having elaborate special adaptations for cross fertili- 

 zation. 



Practical Questions 



1. Why does a strawberry bed sometimes fail to fruit well, although it 

 may flower abundantly? (267, 268.) 



2. Are berries found on all sassafras trees? On all buckthorns? 

 Hollies ? 



3. Would a solitary hop- vine produce fruit? A solitary ash tree-? 

 (267.) 



4. Why is a mistletoe bough with berries on it so much harder to find 

 than one with foliage merely? (267, 268.) 



B. WIND POLLINATION 



MATERIAL. In spring, catkins of forest trees, staminate and pistillate 

 flowers of pine. At nearly all seasons, heads of grain and panicles of va- 

 rious kinds of grass can be obtained. For experiment, a potted plant of 

 any kind, just about to bloom, may be used. 



EXPERIMENT 80. To TEST THE EFFECT OF SHUTTING OUT EXTERNAL 

 AGENCIES. Tie paper bags over flower buds of different kinds when nearly 

 ready to open and leave until the flowers have withered. On removing 

 the bags, mark with colored threads the flowers that had been covered, and 

 watch until seed time. Do you notice any difference in the number, size, 

 or weight of the seed produced by them and by those of the same kind left 

 exposed ? How do you account for the difference, if there is any ? By 

 what agencies could foreign pollen have been carried to the stigmas of 

 the exposed flowers? If any of the covered specimens wither and drop 

 their seed vessels without any attempt to fruit, examine a fresh flower, and 

 see if it is capable of self-pollination. 



As already explained, experiments of this kind, to be conclusive, should 

 be tried on as many specimens as possible. The greater the number of 

 species and individuals included, the better. Where it is not practicable 

 to carry on experiments by the class, pupils who are interested can make 

 them at homo. 



273. The problem of pollination. -- When a plant has pro- 

 vided against self-pollination, its problem is only half solved, 



