6 
ORGANOGRAPHY. 
BOOK I. 
1 
c 
cavities, separated by partitions (Jig, 1.). These little cavities 
are the inside of bladders of cellular tissue ; and the partitions 
are caused by the cohesion of their sides, as may be easily 
proved by boiling the pith a short time, when the bladders 
readily separate from each other. In pulpy fruits, or in those 
which have their cellular tissue in a loose dry state when ripe, 
the bladders may be readily separated from each other without 
boiling. It was formerly thought that cellular tissue might be 
compared to the air bubbles in a lather of soap and water ; 
while by some it has been supposed to be formed by the 
doublings and foldings of a membrane in various directions. 
On both these suppositions, the partitions between the cells 
would be simple, and not composed of two membranes in a 
state of cohesion ; but the facility with which, as has just been 
stated, the cellules may be separated, sufficiently disproves 
these opinions. It is probable, however, that although the 
double nature of the partitions in cellular tissue may be 
demonstrated, yet that the cellules usually grow so firmly 
together, that their sides really form in their union but one 
membrane. 
The bladders of cellular tissue are destitute of all perforation or 
visible pores, so that each is completely closed up from its neigh- 
bour, as far as we can see ; although, as they have the power of 
filtering fluids with rapidity, it is certain that they must abound 
in invisible pores, and that they are not impermeable, as if they 
were made of glass. An opinion different from this has been 
and is still entertained by some observers, who have described 
and figured perforations of the membrane in various plants. 
Mirbel states that " the sides of the bladders are sometimes 
