286 THE FRUIT. 



535. The Pericarp, or Seed-vessel, is the ripened ovary. It 

 should, therefore, accord in structure with the ovary from which 

 it is derived. Yet alterations sometimes take place during fruc- 

 tification, either by the abortion or obliteration of parts, or by 

 accessory growth. 



536. Internal Alterations. Thus, the ovary of the Oak con- 

 sists of three cells, with a pair of ovules in each ; but the fruit 

 has a single cell, filled with a solitary seed, only one ovule being 

 matured, while two cells and five ovules are suppressed, the 

 remains of which may be detected in the acorn. The ovary 

 of the Chestnut has six or seven cells, and a pair of suspended 

 ovules in each ; but only one of the dozen or fourteen ovules 

 ever develops into a seed, except as a rare monstrosity. The 

 three-celled ovary of the Horsechestnut and Buckeye is similar 

 in structure (Fig. 608-611), and seldom 



ripens more than one or two seeds ; but the 



abortive seeds and cells are obvious in the ripe fruit. The 

 ovary of the Birch and of the Elm is two-celled, with a single 

 ovule in each cell : the fruit is one-celled, with a solitary seed ; 

 one of the ovules being uniformly abortive, while the other in 

 enlarging thrusts the dissepiment to one side, and obliterates the 

 empty cell. Similar suppressions in the fruit of parts actually 

 extant in the ovary are not uncommon. 



537. On the other hand, there may be more cells in the fruit 

 than there are primarily in the ovary. Thus the fruit of Datura 

 is dicarpellary and normally two-celled, with a large placenta 

 projecting from the axis far into the cells. But each cell be- 

 comes bilocellate, that is, divided into two, by a false partition 

 growing out from the back of each carpel and cohering with the 

 middle of the adjacent placenta. So the 5-carpellary and nor- 

 mally five-celled ovary of common Flax early becomes spuriously 

 ten-celled (morphologically speaking, not 10-locular, but 10- 

 locellate), by a false partition extending from the back of each 



FIG. 608. Longitudinal section of the ovary of a Buckeye (jEscnlus Pavia), showing 

 the pairs of ovules in two of the cells. 609. Transverse section of the same displaying all 

 three cells and six ovules. 610. Same of half-grown fruit, with single fertile seed, abor- 

 tive ovuleg and obliterating cells. 611. Dehiscent one-seeded fruit, diminished in size. 



