196 COMPOUND ORGANS OF PLANTS. 



it proceeds from a simple carpel or pistil. In this case the 

 pericarp presents constantly one single cell, or it is unilocular. 

 The compound fi'uit proceeds from the compound pistil, the 

 pericarp, like the ovary, containing as many cells as the number 

 of pistils which have united. Thus the pericarp is bi-locular 

 in the tobacco, tri-locular in the tulip, quadri-locular in the 

 epilobium, quinque-locular in flax, &c. We have already made 

 known these particulars in treating of carpels. 



It is necessary to observe here, that the number of cells in 

 the pericarp or ripe fruit, does not always exactly correspond 

 to the structure of the ojary. It often happens, between the 

 moment of fecundation and the maturity of the seed, that con- 

 siderable changes take place in the internal structure of the 

 ovary, a number of its dissepiments being absorbed during its 

 progress towards maturity, so that an ovary originally multilo- 

 cular becomes finally an unilocular fruit or pericarp. A great 

 many of the Caryophyllacese and the Cistaceae are in this case. 

 The rapid increase of their ovaries break and efiFace their disse- 

 piments, so that they are not found in the mature pericarp. 

 Alterations take place, not only in the number of cells, but 

 also in the seeds, the ovules being equally liable to become 

 obliterated. In the acorn, (Fig. 92,) the young pistil is formed 

 of three carpels, the ovary consisting of three cells with two 

 ovules in each cell as represented in the transverse section. 

 But the walls of the cells and five of the ovules are suppressed in 

 the progress of development, so that the pericarp ultimately 

 becomes unilocular and monospermal, or one-seeded. Hence 

 the acorn or fruit of the oak (Quercus), consists of a one-seeded 

 pericarp, surrounded by an involucre of bracts forming the cup 

 or cupula. 



Dehiscence of the pericarp. When the fruit has arrived at a 



