210 APPLIED BIOLOGY 



insects ; and if this is true, grouping of flowers in clusters is 

 surely important. 



Concerning the suggestion above that flower-clusters favor 

 pollination by the wind, it is evident that flowers held above 

 the leaves of a plant have a most advantageous position both 

 for distributing their pollen to the wind and for receiving 

 it from some other plant. Notice a field of grass, oats, wheat, 

 or corn when in flower, and observe how well the flower- 

 clusters are exposed to the wind. Imagine these flowers 

 scattered along the stem where the main leaves are, and it 

 at once becomes clear that the wind could not scatter the 

 pollen widely. 



Finally, the value of flower-clusters for seed-distribution 

 is based on the same facts as cited above for pollination by 

 wind. Any one who has watched the wind scatter the seeds 

 of thistle, dandelion, or trees which have winged seeds, will 

 understand at once how flower-clusters in their usual exposed 

 positions are of great advantage in scattering seeds. 



207. Flowers in Heads. What are commonly called 

 flowers of clover, dandelion, etc., are not single flowers, but 

 clusters of flowers set on the expanded end of a flower-branch 

 (Fig. 66, D). When thus set in heads and crowded closely 

 together, the constituent flowers are very small. A dande- 

 lion flower-head (commonly called dandelion flower), a sun- 

 flower, or some similar flower-head should be examined. 



Dandelion Flower-head. (L) Dandelion plants taken up in fall 

 or early spring are easily grown in pots or boxes in the schoolroom, 

 and flowers in various stages of development obtained. 



Examine the peculiar flower-stem which supports the head of 

 flowers. As the flowers grow old and the head becomes closed by 

 the surrounding bracts, notice whether this flower-stem grows 

 longer, and especially notice its length when the seeds are mature 

 and about to be blown away by the wind. 



Notice that beneath the flower-head are two rows of bracts, 

 collectively forming an involucre. Observe the position of these 

 bracts in young heads, and in old ones which have closed. These 



