CHAPTEK I. 



CELLULAR TISSUE. 



5. This consists of a number of vesicles or bladders, with 

 thin transparent sides adhering together, and containing fluid. 

 A piece of honey-comb gives a very good idea of this tissue 

 when it is at all regular, which is seldom the case, the walls 

 of the cells in the honey-comb representing the sides of the 

 cells in plants, and the inclosed spaces the cavities formed by 

 the union of the cells themselves. To become familiar with 

 this tissue, it is only necessary to examine a thin slice of any 

 of the succulent plants with the microscope, or the pulpy part 

 of an orange, where these cells may be readily distinguished 

 by the naked eye, and separated from the mass of the fruit. 

 When the body is sufficiently transparent, its internal struc- 

 ture may be perceived with the aid of the microscope, without 

 examining it in section. We may sometimes see this cellu- 

 lar structure very distinctly in a piece of thin transparent sea- 

 weed, or " in a young and delicate rootlet," and " observe the 

 closed cavities entirely circumscribed by nearly transparent 

 membranous walls."* 



6. Each cell is in itself a distinct and separate cavity; the 

 wall or partition between two cells is therefore double, being 



* Gray's Botanical Text-Book. 

 2* 



