THE ANGIOSPERMAE 1537 



with septicidal dehiscence, separating two uniovulate portions which are 

 closed and are therefore akenes, just as the separated portions of the septi- 

 cidal fruits, which contain several seeds and do open, are follicles. Capsule 

 and follicle are, in fact, fundamental types among the dry fruits and the 

 rest, except for some akenes, can all be derived from the one or the other. 



Dehiscence in capsule fruits is primarily due to the strains set up by 

 unequal shrinkage of the cell-layers in the pericarp as the fruit dries towards 

 maturity. Drying is assisted by blockage of the water supply, due to 

 thickenings in the pedicel, and furthered by evaporation from the fruit 

 itself and from any attached floral organs, e.g., sepals, which may remain. 

 The lines of dehiscence are predetermined by lines of weakness formed of 

 thin-walled cells in the pericarp, either at the sutures or along the median 

 line of the carpels. Circumscissile dehiscence is also determined by a 

 mechanically weak zone, due either to the alignment, or the size or the 

 state of thickening of the cells, or their meristematic condition, or by a 

 combination of these factors. A typical case is that of Portulaca oleracea, 

 where dehiscence takes place along a zone of thin-walled cells, lying 

 between two zones of sclerenchyma. In Anagallis, Sesuvium and some 

 others the thin-walled layer remains meristematic. 



II. Fleshy Fruits 



Manifold in appearance as these are, their classification is relatively 

 simple, for they fall into two main types only, neither of which is truly 

 dehiscent, though partial splitting may occur. 



I. Berries. Here the pericarp is usually massive, soft, juicy and short- 

 lived. It is formed of three distinct layers. Outermost comes 

 the skin or epicarp, which generally colours conspicuously when 

 ripe. Within this is the comparatively thick flesh, or rnesocarp, 

 and innermost is the membranous endocarp. The whole encloses 

 the seeds, which are rarely solitary [Myristica, Phoenix), and may 

 be numerous. The berries of Actaea (Ranunculaceae), Arum and 

 Berberis are formed from a single carpel ; Atropa, many other 

 Solanaceae and J'itis have berries of two carpels; Convallaria 

 and Asparagus, berries of three carpels; in Actinidia (Chinese 

 Gooseberry) of many carpels. The pericarp is sometimes rela- 

 tively thin, though soft, as in Galium, forming a transition to the 

 capsule. Indeed the berry diflFers from the capsule principally 

 by its soft pericarp and there are some types which might be 

 considered as belonging to either category, e.g.. Capsicum, Podo- 

 phyllum (Fig. 1399), Lardizabala. The berry of Myristica, 

 although unicarpellary, dehisces to expose the single seed. 



It might be logical but it would be a rediictio ad absurdum to separate 

 the berries formed from inferior ovaries as "false fruits", most of them 

 being perfectly typical berries. In this category we have Cojfea, two carpels; 

 Sambucus, three carpels; Hedera, five carpels and Ribes (Gooseberry) with 



