594 CONSERVATIVE ORGANS. [LECT. X. 



tiuctly perceive the nature of their conjunction 

 (b.b.); but no projecting tubular processes. The 

 spaces, such as a. a. are filled with air in the same 

 manner as the vacuities in the leaves of aquatic 

 plants. In what manner then do the cells commu- 

 nicate? To answer this question properly, we ought 

 to understand the structure of the intercellular 

 membrane. But here our instruments fail, if 

 they do not mislead us ; and, under glass.es of the 

 highest power, this membrane appears different 

 under different circumstances : by transmitted light, 

 it seems a simple, unorganized, transparent pel- 

 licle ; but, by reflected light, is evidently porous. 

 I have already stated my belief that the cells of 

 the stem communicate by pores, and I see no 

 reason for altering this opinion with regard to 

 those of the leaf: although I do not concur in 

 opinion with M. Mirbel and Sprengel, that the 

 form, position, magnitude, and number of these 

 pores can be determined. An opinion has been 

 advanced, that the fluids may be transmitted 

 from cell to cell, " consistently with the integrity 

 of the cellular structure," by the exercise of the 

 alternate functions of secretion and absorp- 

 tion;" but these functions imply the existence of 

 either glands or vessels connected with the absorb- 

 ing and secreting surface, which are, however, 

 even less demonstrable than the pores. Upon the 

 whole, the question is still unanswered; and all 



