CROSS-POLLINATION 



91 



stigroct 

 anther 



pollen. 



PROBLEM X. WHAT ARE SOME SPECIFIC EXAMPLES OF 

 CROSS-POLLINATION ? 



Demonstration. Some of the material in the following paragraphs 

 will be available for study. If possible, supplement the text with charts 

 which can be used as a basis for discussion. Snapdragon may be sub- 

 stituted for butter-and-eggs. 



Butter-and-eggs. From July to October in the East, the very 

 abundant weed called " butter-and-eggs " may be found, especially 

 along roadsides and in sunny fields. It bears a tall and con- 

 spicuous cluster of yel- 

 low and orange flowers 

 known to botanists as 

 a spike, the flowers 

 being arranged so that 

 they come out directly 

 on main stalk. 



The corolla projects 

 into a spur on the 

 lower side; an upper 

 two-parted lip shuts 

 down upon a lower 

 three-parted lip. The 

 four stamens are in 

 pairs, two long and 

 two short. 



Certain parts of the 

 corolla are more brightly colored than the rest of the flower. 

 Butter-and-eggs is visited by bumblebees, which apparently 

 are guided by the orange lip to alight just where they can 

 push their way into the flower. The bee, seeking the nectar 

 secreted in the spur, brushes its head and thorax against the 

 stamens. It may then, as it pushes down after nectar, leave 

 some pollen upon the pistil, thus effecting self-pollination. Later 

 in visiting another flower of the same kind, the bee may leave 

 some of the pollen of the first flower on the pistil of the second 

 flower, thus causing cross-pollination. 



„nectccr 



By means of the text and diagram explain how the bee 

 transfers pollen from one flower to another of " butter-and- 

 eggs." 



