DISPERSAL OF FRUITS AND SEEDS 369 



the longitudinal splitting of the dry capsule, as this kind 

 of fruit is called. In other cases the top of the capsule 

 comes off along a horizontal line (pimpernel) . Sometimes 

 the capsule opens by pores in the wall (poppy) , out of 

 which the very small seeds are shaken when the stem 

 is swayed by the wind, by which they may be carried 

 a considerable distance from the parent plant. 



Methods of Fruit and Seed Dispersal, (i) Dispersal 

 by Wind. — This is a very common means of dispersal. 

 Seeds and dry one-seeded fruits vary very much in the 

 distance they may be blown. The smaller the seed 

 or fruit the further it will be carried, if the shape and 

 the specific gravity are the same, because the smaller 

 the seed the greater the ratio of surface to bulk. Many 

 small seeds are carried for some distance in this way. 

 On the other hand, a large seed like the broad bean 

 is scarcely affected by the wind and simply drops out 

 of the pod. If a seed is flat instead of being round, 

 its surface wUl be greatly increased, and it will blow 

 much further. Many seeds and one-seeded fruits 

 bear outgrowths from the testa or pericarp, which greatly 

 increase the surface on which the wind can act. These 

 are of two main MT\.d.s— wings and hairs (plumes). 



Winged fruits are pretty common. A well-known 

 example is the sycamore fruit. There are two joined 

 carpels in the flower, and from the free side of 

 each a curved wing grows out. When the fruit is 

 ripe the two carpels split apart, and the two are often 

 detached from the tree separately. The shape of the 

 wing causes the one-seeded " mericarp " (separated 

 part of the whole fruit) to spin as it falls, and it is thus 

 more likely to be carried away by the wind. Other 

 examples of winged one-seeded fruits are those of the ash 

 (" keys "), the birch, and the hornbeam. In the last two 



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