140 MORPHOLOGY, OB COMPARATIVE ANATOMY. 



become blended with the ovary or ovaries to form the fruit ; and a still 

 more complex kind of fruit is formed by all the flowers of an inflo- 

 rescence becoming conjoined into a common structure during the ripening 

 of the seed, so as to form a collective fruit, such as occurs in the Pine- 

 apple (fig. 308), Mulberry (fig. 307), Bread-fruit, the Fig (fig. 306), 

 cones of Firs, &c. 



Considered as developments of the carpels alone, many fruits in their 

 mature condition depart widely in appearance from the ovaries from 

 which they are produced, the morphology of fruits exhibiting perhaps 

 more remarkable cases of actual metamorphosis than any other parts of 

 plants. Hence it is often difficult to judge from a fruit what kind of 

 pistil the flower has possessed, and the structure of fruits can only be 

 understood by a study of their progressive development from the imma- 

 ture to the mature condition. 



The most important source of change is the suppression of chambers or 

 loculi of the ovary, together with the abortion of ovules. Thus the flower 

 of the Birch has a two-celled ovary with one ovule in each cell ; but one 

 cell with its ovule is constantly abortive and almost entirely disappears in 



Fig. 271. Fig. 272. 



Fig. 271. Female flower of the Oak: a, vertical section; b, cross section. 

 Fig. 272. Fruit of the Lime (Tilia) : a, entire ; b, cross section. 



the fruit. In the female flower of the Oak and hazel-nut there are three 

 cells, each with two ovules (tig. 271) ; but only one cell is found in the ripe 

 fruit, and this is filled by one solitary remaining seed, as we find in the 

 Acorn or nut. In the Lime there are several cells in the ovary, but gene- 

 rally all but one are obliterated in the fruit (fig. 272) ; and similar cases are 

 by no means uncommon. In these cases the dissepiments, called in the 

 fruit septa, are not broken down, but pushed to one side and obliterated 

 by the pressure exercised by the developed seed. 



On the other hand spurious partitions are sometimes formed, as in 

 Datura Stramonium, which has a four-celled fruit derived from a two- 

 celled ovary : and in the pods of Legumiiiosae cross partitions are often 

 produced between the seeds. 



The original conditions are frequently still further concealed by the 

 alterations in the texture of the coverings of the fruit, next to be de- 

 scribed. 



The Pericarp. The " wall " of the fruit is the substance formed 

 from the carpels, or (when present) from the other component 



