ORGANOGRAPHY. 



BOOK I. 



cavities, separated by partitions {fig. 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 pidi 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 

 m nivisible pores, and that they are not impermeable, as if they 

 were made of glass. An opinion diiferent from this has been 

 and is still entertained by some observers, who have described 

 and figured perforations of the membrane in various plants 

 Mnbel states that " the sides of the bladders are sometimes 



