82 MORPHOLOGY. 
The wall of the ovary which becomes developed to form the 
seed-vessel is called the pericarp (pericarpium'). On the latter, 
from the exterior to the interior, there may often be distin- 
guished three layers, differing in their structure or their color, 
the epicarp (epicarpium ’), mesocarp (mesocarpium *), and endo- 
carp (endocarpium’). 
The outer coating of the fruit often shows completely the 
structure of the epidermis, 7. ¢., it isprovided with a very strong 
cuticle and with stomata; often, however, it is formed to a 
predominating extent of stone-cells (sclerenchyma). The variety 
of the tissues and their contents is still greater in the middle 
layer (mesocarp), which in many fruits consists of fleshy, juicy, 
or even very loose tissue. When its cells contain an abundance 
of juice and finally lose their coherence, it is designated as pulp, 
: Fia. 17,—Cé ium maculatum. a, endosperm ; c, commissural surface ; r, coste or, 
ribs with the vascular bundles (f v); f, vallecule or grooves (Hager). 
as, é. g. in the legume of the tamarind. The inner layer of the 
fruit (endocarp) originates from the epidermis of the cavity of 
the ovary, and often develops into a hard stone-shell, as in the 
case of the almond. It is, however, not always the case that a 
discrimination can be made between the three layers of the 
ripened seed-vessel, and their relative development is very 
variable. 
Of aggregations and forms of fruits, the following are distin- 
guished : 
' IZept about or around, xapzds fruit. 
*Exi upon. 
4 Mé6os in the middle. 
* Evdor within. 
