407 
Physiology of Pulpy Fruits. 
Externally these are bounded by the epidermis, but internally 
they pass into an inner zone of tissue, which lines the cavity 
of the ovary, and which consists of very small cells which form 
a somewhat misty-looking layer. It is from the last-mentioned 
tissue that the stony endocarp is formed which renders the 
examination of all but very immature fruits a matter of con- 
siderable difficulty. The number of cells does not increase 
greatly, the divisions which do occur are mainly transverse to 
the long axis of the fruit ; tangential divisions are very rare, 
except in the peripheral cells, which ultimately form the 
epicarp, although even here they are by no means of common 
occurrence. 
As the drupes increase in size after the flower has withered, 
they are unable to expand equally in all directions owing to 
the mutual pressure consequent on their crowded condition, and 
hence each is broadest at its upper portion (PI. XXV, Fig. 20). 
When differentiation begins in the pericarp, those cells which 
finally give rise to the endocarp are the first to become special- 
ized. These cells consist of fibres so elongated that a chain 
of such fibres running round the fruit cavity resembles a seg- 
mented ring or hoop. Owing to the regularity with which 
the cells fit into one another, this appearance is rendered most 
strikingly prominent, and the whole of the interior of the ovary 
appears to be bounded by these c rings, 5 which run in a trans- 
verse direction round it. Only a part of the endocarp, how- 
ever, forms these transversal rings, the rest consists of fibres, 
also regularly arranged, but whose longest axis runs in a 
direction at right angles to that of the cells just described. 
The result of this arrangement is that the ovarian cavity is 
protected by a band of tissue, of which one half is fitted to 
stand strains and stresses in one direction, while the other 
half is equally well capable of resisting similar strains and 
stresses in a direction at right angles with the first. The 
regularity of the two systems is somewhat broken by subse- 
quent changes due to growth, but the general formation is 
sufficiently obvious even in ripe fruits. The endocarp, when 
differentiated, rapidly increases in thickness in the way I have 
