FRUITS AND SEEDS 113 



(Fig. 81, c). This type of fruit is characteristic of the family 

 Leguminosce (page 351). 



(d) The silique is a pod derived from two carpels, which 

 separate at maturity, leaving partition walls, as in the case of 

 the mustard and related plants (Fig. 81, d). It is character- 

 istic of the family Cruciferce (page 341). 



(e) The pyxidium or pyxis is a capsule which opens by 

 means of a lid, as in the plantain (Fig. 81, e). 



Seeds. Seeds are borne within the ovary and should not 

 be confused with fruits. In fact, there is very little reason for 

 confusion except in the case of the indehiscent fruits, especially 

 the achenes and caryopsis, which are usually referred to as 

 seeds. We very generally but incorrectly speak of grains of 

 corn or wheat as seeds, but they are true indehiscent fruits. A 

 knowledge of their structure will make this point perfectly clear 

 to any careful student of botany. We have already studied the 

 formation of seeds in connection with reproduction (page 98), 

 and they will receive further consideration in the next chapter. 



SEED DISTRIBUTION 



Unless there is some natural method for scattering seeds 

 from place to place any species would remain in a very restricted 

 locality indefinitely. But we know that the range of plants is 

 extended by the scattering of the seeds. If they were not scat- 

 tered, they would fall directly beneath the parent plant, and the 

 young plants would be so crowded that they could not develop 

 normally. The most common methods are as follows: 



(a) Seed Dispersal by the Wmd. Many seeds possess struc- 

 tures which act as wings or floats by which they are carried for 

 long distances. Some of the common forms with wings are the 

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