428 FOURTH GROUP.— SEED-PLAXTS. 



Two principal forms of true fruits each with two subordinate forms may be distin- 

 guished for purposes of classification and in conformity with the traditional terminology, 

 according as the pericarp in the ripe state has fleshy, succulent layers or not, and 

 according as the ripe fruit opens to discharge the seeds which become detached from 

 the placentas or remains closed, namely : 



A. Dry fruits : pericarp woody or tough and leathery, the cell-sap having disappeared 

 from all its cells. 



1. Dry indehiscent fruits : the pericarp does not open, but envelopes the 



seed till germination ; the seed-coat is thin and membranous, and little 

 developed, 

 (n) One-seeded dry indehiscent fruits fachenial-fruits) :- 



The nut (glans) : the dry pericarp is thick and hard, and is composed of 

 lignified sclerenchymatous tissue, as in Coryliis. 



The achetie and caryopsis : the dry pericarp is thin, tough and leathery, 

 closely surrounding the seed and separable (true achene) or not (caryopsis) 

 from the seed-coat, as in Ranunculus, the Gramineae, and Compositae. 

 ^i) Bilocular, or plurilocular dry indehiscent fruits : — 



These usually separate into mericarps, that is, are schizocarps, each re- 

 sembling a nut or achene, as in Umbelliferae and Geraniaceae ; in Ace}' the 

 mericarp is winged and termed a safnara. 



2. Dry dehiscent fruits (capsular fruits) : the pericarp dehisces when fully ripe 



to release the seeds, which are in this case themselves clothed with a strongly 

 developed usually hard or tough seed-coat ; the fruits have usually more seeds 

 than one. 

 (<i) Capsular fruits with longitudinal dehiscence : — 



The follicle consists of a single carpel which opens along the coherent 

 margins (the suture) which bear the seeds, as in Paeonia and Illicium 

 anisatuvi ; in Asclepias the thick placenta is also detached. 



The legume consists also of a single carpel, which opens not only along the 

 ventral suture but also along the dorsal median line, and thus separates into 

 longitudinal halves, as in Pliaseolns and Pisum. 



The siliqua consists of two carpels which form a bilocular fruit with 

 a longitudinal (spurious) dissepiment ; the pericarp opens by two valves which 

 separate from the united margins of the carpels (replum) ; between these is 

 the stretched dissepiment which remains behind, as in the Cruciferae. 



The capsule in the narrower use of the word is formed from a polymerous 

 unilocular or plurilocular ovary, and parts longitudinally into two or more 

 valves which separate part of the way from the apex downwards, as in 

 Cerastium, or down to the base. If the longitudinal fissures pass through 

 the dissepiments in a plurilocular fruit, the dehiscence is septicidal, as in 

 Colchicum ; but if the fissure is in the middle between each pair of dissepi- 

 ments, the dehiscence is loculicidal, as in Tulipa and Hibiscus \ in these 

 cases a half dissepiment may remain attached to each edge or an entire 

 dissepiment may remain attached to the middle of each valve ; but if a part 

 of each dissepiment or the entire dissepiments remain attached to a central 

 column, which is thus winged and from which the valves are detached, the 

 dehiscence is septifragal, septicidally or marginicidally septifragal, as in 

 Calluna and Rhododendro7i, or locucidally septifragal, as in Datura. If 

 the capsule comes from an unilocular polymerous ovary, the separation of the 

 valves may take place in the sutures and correspond to the septicidal 

 dehiscence, as in Ceniiana, or midway between them and answer to the 

 loculicidal dehiscence, as in Viola. 

 {^) Capsular fruits with transverse dehiscence : — 



The pyxidium or circumscissile capsule opens by the separation of 



