THE PERICARP. TES 
ovaries of which have several cells and ovules, the fruit has 
only one cell, and frequently only one seed. 
»479. The dissepimerits of a many-celled pericarp often 
become contracted, 6 as merely to project into the general 
cavity, the placenté being placed upon their edges and 
called parietal, as in Poppy. Or it may be supposed that the 
margins of each carpel have not united, and do not reach to 
the centre or axis of the pericarp, the placenta being then 
placed upon the united margins of the adjacent sides of two 
carpels. In the melon, the carpels are scarcely folded in- 
wards, and the cells are not separate. In the Thorn Apple, — 
(Datura Stramonium), two of the dissepiments are imperfect 
at the upper part, forming a communication between the 
cells, which are quite separate inferiorly. The dissepiments 
in these cases are called incomplete. Spurious or false dis. 
sepiments are those formed by enlargements of the placenta, 
or irregular projections from the back or sides of the peri- 
carp (Cassia fistula): when horizontal they are sometimes 
called phragmata. 
480. When the pericarp does not open spontaneously when 
ripe to let the seed escape, it is called indehiscent. When 
there are natural slits or openings by which the seed can 
escape, the pericarp is said to be dehiscent, and the pieces into 
which it divides are called valves. It is bivalved, trivalved, 
&e. according to the number of valves into which it splits. 
481. Pericarps which are formed of a single carpel or 
modified leaf, have on their surface two well marked lines 
or sutures, by which they easily dehisce. One is called dor- 
sal, and occupies the place of the midrib of the leaf which 
became the carpel. The other is called ventral, and cor- — 
responds to the united margins of the leaf, where the pla- 
cehta is situated. The pod of the Pea has a dorsal and ven- 
tral-suture, both well marked. In shelling peas it is the 
-suture by which they are opened, and the pé 
seeds will be observed placed on a thin placenta at the op- 
opled or ventral suture. Ih the pabg pericarp, 
