THE FRUIT. 



51 



145. As a rule, the structure of the fruit agrees essentially 

 with that of the ovary. In many cases, however, the fruit un- 

 dergoes such changes in the course of its growth from the ovary 

 as to disguise its real structure. An early examination, there- 

 fore, is always more reliable in its results than a late one. For 

 example, the Oak-acorn is a fruit with but one cell and one 

 seed, although its ovary had three cells and six ovules ! This 

 singular change is due to the non-development of five of its 

 ovules, while the sixth grew the more rapidly, obliterated the 

 partitions by pressing them to the wall, and filled the whole 

 space itself. Similar changes characterize the Chestnut, Haz^l- 

 nut, and that whole Order. The ovary of 

 the Birch is 2-celled, 2-ovuled ; but by the 

 suppression of one cell with its ovule, the 

 fruit becomes 1-celled and 1-seeded. 



1&4 



163 



162 Section of the ovary of an Acorn, 3-celled, 6-ovuled. 163, Section of ovary of Birch 2-celled 

 2-ovuled 164. Vertical section of the same in fruit. 165, Pericarp of Mi K n,>nette open son,, after now' 

 ermg. 100, JNaked seed of Taxus Canadeusis, surrounded, not covered, by the fleshy pericarp. 



On the other hand, the cells are sometimes multiplied in the fruit by the formation of 

 false partitions. Thus the pod of Thornapple (Datura) becomes 4-celled from a 2-celled 

 ovary ; and the longer pods of some Leguminous plants have cross-partitions formed 

 between the seeds. 



146. The Pericarp. The fruit consists of the pericarp and 

 the seed. The pericarp (xgpi, around) is the envelope of the 

 seeds, consisting of the carpels and whatever other parts they 

 maybe combined with. It varies greatly in texture and -sub- 

 stance when mature, being then either dry, as the Pea-pod, or 

 succulent, as the Currant. Dry pericarps are membranous, or 

 coriaceous (leathery), or woody. Succulent pericarps may be 

 either wholly so, as the Grape, or partly so, as the Peach and 

 other stone fruit. 



147. With very few exceptions the pericarp encloses the seed 

 while maturing. In Mignonette (105), however, it opens, ex- 



