43 



acid. When perfectly dry it was carefully examined under a high 

 power, and the membrane, which we are not to forget was originally 

 discovered by Dr. Brown without the application of heat, appeared 

 distinctly organized, extending along and beyond the margin of the 

 stoma, and uniting, almost after the manner of lips, in the enclosed 

 oval space. 



These labia, where they existed, became more evident after the 

 process of charring ; which process, in the particular example now 

 alluded to, was so conducted as to obviate all error arising from pres- 

 sure. The tissue was placed on a slip of glass, and submitted to the 

 action of heat, without being covered by another slip. Thus both 

 the supposed sources of error are avoided ; the one, by the previous 

 removal of organic mucus ; and the other by a different manipulation. 



Mr. Lens Aldous has furnished me with a sketch of these membra- 

 nous labia of the stomata under the direction of Mr. Bowerbank, (PI. 

 i. fig. 3). The power employed was about 2000 linear; and I may 

 be permitted to add that Dr. Williams, after seeing the membrane 

 under this power, immediately approved of the process which ren- 

 dered it so distinctly visible. 



Stone Vicarage, 



November 20, 1841. 



