I 
CHAP. II. 
FRUIT. 
189 
In septifragal dehiscence the dissepiments 
adhere to the axis and separate from the 
valves, as in Convolvulus ; or in the dia- 
gram 170., lettered as before. 
In sutural dehiscence there are no disse- 
piments, the fruit being composed of only 
one carpel, as the pea. 
Besides these regular forms of valvular dehiscence, there is 
a mode which obtains in a very few plants, called circumscissile. 
This occurs by a transverse circular separation, as in Ana- 
gallis ; in JefFersonia it only takes place half round the fruit. 
Valvular dehiscence, which is by far the most common 
mode by which pericarps open, must not be confounded with 
either rupturing or solubility, — irregular and unusual con- 
trivances of nature for facilitating the dispersion of seeds. In 
valvular dehiscence the openings have a certain reference to 
the cells, as has been already shown ; but neither rupturing 
nor solubility bear any distinct relation to the cells. Rup- 
turing consists in a spontaneous contraction of a portion of the 
pericarp, by which its texture is broken through, and holes 
formed, as in Antirrhinum and Campanula. Solubility arises 
from the presence of certain transverse contractions of a one- 
celled pericarp, through which it finally separates into several 
closed portions, as in Ornithopus. 
For the nature of the placenta and umbilical cord see the 
observations under ovary. These parts, which are mere 
modifications of each other, essentially appertain to the peri- 
carp, in which the former often acquires a spongy dilated sub- 
stance, occasionally^ dividing the cells by spurious dissepi- 
ments, and often giving to the fruit an appearance much at 
variance with its true nature. In some seeds, as Euonymus 
Europaeus, it becomes exceedingly dilated around each seed, 
forming an additional envelope, called aril. The true charac- 
ter of this organ was unknown till it was settled by Richard : 
before his time the term was applied, not only in its true sense 
to an enlargement of the placenta, but also to the endocarp of 
certain Rubiaceae and Rutaceae, to the seed coat of Jasminum, 
Orchideae, and others, and even to the perianth of Carex. A 
very remarkable instance of the aril is to be found in the nutmeg. 
