Fig. 243.—Fruit of Raspberry.
Fruits that are formed by the subsequent union of separate pistils are aggregate fruits. The carpels in aggregate fruits are usually more or less fleshy. In the raspberry and the blackberry flower, the pistils are essentially distinct, but as the pistils ripen they cohere and form one body (Figs. [243], [244]).
Fig. 244.—Aggregate Fruit of Mulberry; and a separate fruit.
Each of the carpels or pistils in the raspberry and the blackberry is a little drupe or drupelet. In the raspberry the entire fruit separates from the torus, leaving the torus on the plant. In the blackberry and the dewberry the fruit adheres to the torus, and the two are removed together when the fruit is picked.
Accessory Fruits.—When the pericarp and some other part grow together, the fruit is said to be accessory or reënforced. An example is the strawberry (Fig. [245]). The edible part is a greatly enlarged torus, and the pericarps are akenes embedded in it. These akenes are commonly called seeds.
Fig. 245.—Strawberry; fleshy torus in which akenes are embedded.
Various kinds of reënforced fruits have received special names. One of these is the hip, characteristic of roses. In this case, the torus is deep and hollow, like an urn, and the separate akenes are borne inside it. The mouth of the receptacle may close, and the walls sometimes become fleshy; the fruit may then be mistaken for a berry. The fruit of the pear, apple, and quince is known as a pome. In this case the five united carpels are completely buried in the hollow torus, and the torus makes most of the edible part of the ripe fruit, while the pistils are represented by the core (Fig. [246]). Observe the sepals on the top of the torus (apex of the fruit) in Fig. [246]. Note the outlines of the embedded pericarp in Fig. [247].