LECT. VII.] ANATOMY OF STEMS. 373 



and Kieser * have demonstrated to be the case-f-. 

 2. This membrane must be cribriform, such as I 

 have described it, when seen under the microscope, 

 to permit the aqueous fluid to pass readily through 

 it, and to admit the air into the cells to supply its 

 place. But it is necessary to remark here, that 

 this fact, although supported by the observations 

 of Sprengel, Mirbel, and others, is positively de- 

 nied both by Link and Kieser ; but, as it was re- 

 quisite for those who denied the porosity of the 

 membrane to state how fluids can be transmitted 

 from one cell to another, Link has advanced the 

 unphilosophical suggestion, that this is effected by 

 a double filtration through invisible pores: and 

 the ingenious Mr. Ellis, who gives credit to Kieser's 

 observations, is forced to admit that this filtration 

 can be accomplished, " consistently with the in- 

 " tegrity of the cellular texture, only by the ex- 

 " ercise of the alternate functions of secretion and 

 " absorption J." 3. The mass must be free from 

 any external pressure, which would, eventually, 

 destroy the regular form of the cell. 



It is not easy to conjecture by what means 



* Mem. sur I' Organization des Plantes, p. 91. 



f We may also regard as an analogical proof a fact lately 

 ascertained by Dr. Barclay, that each side of every cell in the 

 honeycomb is double, or composed of two plates of wax. Vide 

 Wernerian Trans, vol. ii. 



J Supplement to the Encyclop. Brit. vol. i. Part 2. 

 BB3 



