THE FRUIT. 123 
the leaves do—absorb a portion of oxygen, and replace it by 
carbonic acid. Fruits seem in all cases to exert a similar’ 
action on the air, the presence of oxygen, and evolution of 
carbonic acid being essential to their ripening. 
470. When fecundation has been effected, the stamens 
and floral envelope, and also the style and stigma, are of no 
further use. They generally wither and fall off, though oc- 
casionally one or more are persistent. The calyx frequent- 
ly forms a covering for the ovary, as in those cases where 
the ovary is inferior, asin the Apple ; the stigma frequently 
_ Yemains, as in the Poppy. The ovary, of course, constantly 
remains, and forms the future pericarp or covering of the 
seed, while the ovule becomes the seed. 
CHAP. IV.—THE FRUIT. 
471. Tue fruit is : aoe of the ovary and its contents, 
arrived at maturity by the fecundating influence of the pol- 
len; and consists of two parts, the pericarp or covering, 
which i is the ovary matured, and the seed, which is the ovule 
matured. When the ovary is inferior, the external part of 
the pericarp is formed of the tube of the calyx. 
I. THE PERICARP. i f 
472. This organ is almost invariably present, but some- 
times remarkably thin, as in the Umbellifere and Composi- 
~ tes and in the Conifer and Cycadee is altogether want- 
ing, these being destitute of ovary. 
473. The part by which it is attached to the peduncle 2 
called the base. The other extremity is the apex 
_ avenlly exhibits traces of the style or stigma. The 
