THE AKENE OR ACHENIUM 



121 



Mericarps are of three classes: (I) The Coelospermous, characterized 

 by the possession by the seed of a concave face (Fig. 337, a); (2) the 

 Campylospermous, characterized by the possession of a longitudinally 

 grooved face (Fig. 338, a); and (3) the Orthospermous, possessing a 

 plane face (Fig. 335) . 



The Silicle. — (See Silique.) 



The Samara. — An indehiscent fruit with a winged pericarp. They 

 are commonly one-seeded, as well as one-carpelled, but may be more. 

 Typically, it is the ovarian wall or the tube of an adnate calyx which 

 develops the wing, but there is no reason why the term should not be 

 extended to include similarly transportable fruits with wings consisting 

 of the accrescent limb of a calyx (Figs. 288 and 289), or corolla (Fig. 291), 

 or a surrounding alate bract (Fig. 292). Commonly the samara possesses 

 but a single wing, unilateral, as in the ash (Fig. 339), or circular, as in 

 the elm (Fig. 287), but not rarely more than one wing is present, as in 

 the maple (Fig. 340), or many Malpighiaceae (Fig. 342). 



--a 



33S 



336 



—a. 



337 



33(9. 



Fig. 335. Transverse section of an orttfl^^permous mericarp: a, vitta; h, rib. 336. Dorsally com- 

 pressed mericarp, two of the ribs winged. 337. Coelospermous mericarp of coriander. 338. Campylo- 

 spermous mericarp of Coniutn. 



The Utricle (Fig. 341). — A one-seeded indehiscent fruit, the seed 

 enclosed in a thin, bladdery or inflated pericarp. It is commonly one- 

 celled, but occasionally several-celled. Ordinarily, utricles eventually 

 become irregularly ruptured, but in a few forms there is a regular 

 ventral opening, approaching toward dehiscence. 



The Akene or Achenium (Figs. 74 to 80 and 344). — A small, indehiscent, 

 one-seeded, seed-like fruit, the pericarp somewhat thickened and 

 entirely distinct from the enclosed seed. The akene varies in many 

 directions toward other fruits. In many cases the pericarp is inclined 

 to be fleshy and in a few it tends toward dehiscence, thus simulating a 



