STRUCTURE.] CELLULAR TISSUE. 27 



hexagonal cavities, separated by partitions (fig. 3). These 

 little cavities are the inside of bladders of cellular tissue ; and 

 the partitions seem to be caused by the cohesion of their 

 sides, for if we boil the pith for a short time, the bladders 

 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 even be 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. But although the double nature of the par- 

 titions in cellular tissue may be often demonstrated, yet the 

 cellules usually grow so firmly together, that their sides really 

 form in their union but one membrane ; and it will be here- 

 after seen that in many cases the partition between two cells 

 is originally simple. 



The cellular being regarded as the type of all other forms 

 of tissue, the attention of anatomists has for a long time 

 been directed to ascertaining in what manner it is originally 

 produced. The nature of this inquiry is such, that great 

 differences in opinion still continue to exist, as to a variety 

 of points connected with it ; and I do not think that we are 

 yet in a condition to form any positive conclusion upon so 

 difficult and obscure a point. The question is, however, one 

 of so much interest that it seems desirable to explain at 

 some length the views of the more experienced and sagacious 

 of the observers who have devoted themselves to its investi- 

 gation. In doing thus, I shall state the case in the form in 

 which it stands in my "Elements of Botany " p. 10. 



A. Cells are produced by gaseous matter extricated among 

 mucus. This is the idea which would strike all observers 

 upon the examination of cellular tissue, with even the naked 

 eye. We remember that it was formerly (about the year 

 1820), the opinion of Francis Bauer, and it is not yet certain 



