388 The Living Plant 



to their seeds such devices as shall make them expose a great 

 surface in proportion to weight, and this they have done in mani- 

 fold ways. 



The simplest way of causing a seed to expose much surface to 

 wind lies hi the addition of a broad flat sail, or a wing. Everybody 

 knows the seed of the Maple, with the lengthened wing growing 

 out from the wall of the fruit (figure 156), and the Elm, with a 

 similar wing except that it encircles the fruit. The conspicuous 





Fio. 156. Winged fruit 



of a Maple. FIG. 157. Winged fruits of the Linden. 



way in which these seeds in their season are blown about our 

 streets proves the efficiency of the arrangement. The seeds of 

 the Linden, or Basswood, are likewise transported by a very fine 

 wing, made from a bract grown fast to the stalk (figure 157), 

 while in Pine and Catalpa the wings grow out from the coats of 

 the seed. These are representative examples; and there are 

 others as well, but less common, in which the wing is supplied 

 by calyx or corolla. 



Acting like the wings, and in some ways still more simple and 

 effective, are large bladders, in which the seeds lie. Some ap- 

 proach thereto is made by those kinds of the Pea Family which 

 have pods greatly swollen but very small seeds; but it reaches 

 more typical development in cases like the Bladder Nut, where 



