THE FRUIT. 



451 



II. Indehiscent Fruits. 



869. The akene. The thin dry wall of the ovary encloses 

 the single seed. It usually does not open and free the seed 

 within. Such a fruit is an akene. An akene is 



a dry, indehiscent fruit. All of the crowded but 



separate pistils in the buttercup flower when ripe 



make a head of akenes, which form the fruit of 



the buttercup. Other examples of akenes are Fig. 472. 



found in other members of the buttercup family, of buttercup. 6 ' 



also in the composites, etc. The sunflower seed 



is a good example of an akene. 



870. The samara. The winged fruits of the maple (fig. 574), 

 elm, etc., are indehiscent fruits. They are sometimes called 



key fruits. 



871. The caryopsis is a dry 

 fruit in which the seed is con- 

 solidated with the wall of the 

 ovary, as in the wheat, corn, 

 and other grasses. 



872. The schizocarp is a 

 dry fruit consisting of several 

 locules (from a syncarpons 

 gyncecium). At maturity the 



carpels separate from each other, but do not themselves dehisce 

 and free the seed, as in the carrot family, mallow family. 



873. The acorn. The acorn fruit consists of the acorn and 

 the "cup" at the base in which the acorn sits. The cup is a 

 curious structure, and is supposed to be composed of an involucre 

 of numerous small leaves at the base of the pistillate flower, 

 which become consolidated into a hard cup-shaped body. When 

 the acorn is ripe it easily separates from the cup, but the hard 

 pericarp forming the "shell" of the acorn remains closed. Frost 

 may cause it to crack, but very often the pericarp is split open at 

 the smaller end by wedge-like pressure exerted by the emerging 

 radicle during germination. 



Fig. 473- 

 Fruit of red oak. An acorn. 



