547 
APPENDIX. 
Page 10. 
The only case of undoubtedly perforated parenchyma with 
which I am acquainted is in Sphagnum, where it was first noticed 
by Mr. Valentine {Muscologia Nottinghamiensis, No. 1. 1833). 
He correctly describes this genus as having the exterior cells 
of its branches furnished with an aperture communicating with the 
external air. The aperture is tolerably distinct in S. acutifolium ; 
it is situated at the upper end of the cell, and stands off obliquely, 
appearing like a minute truncated cone. An easy way to observe 
it is, to press out the air contained in the cells, which escapes from 
the aperture in a minute bubble.” This curious contrivance 
might have been supposed analogous to the air passages into the 
trunk, below the insertion of the leaves of Tree Ferns, if it did 
not equally exist in all the parenchyma of the leaves themselves. 
Mr. Valentine does not notice the latter fact, and I believe he 
considers the circles in the leaves of Sphagnum not to be aper- 
tures: ^but I had ascertained, by Mr. Reade’s ingenious charring 
process, that they undoubtedly are openings, before I saw John 
Roper’s paper upon the subject in the Annales des Sciences (n. s. 
X. 314.). This writer determined that the circular spaces in 
Sphagnum leaves are openings, by observing the exit and entrance 
through them of the Rotifer vulgaris, and of minute granular matter. 
He considers the openings intended to guarantee the organs of 
respiration from the too great influence of the air.” But I do not 
perceive in what way such an effect is to be accomplished. 
Page 32. 
Spiral vessels certainly exist in the roots of many exogens ; 
in the Parsnep and the Beet they are large, and readily extracted 
entire. 
With regard to their existence in seeds, Mr. Quekett has 
favoured me with the following memorandum (March 13. 1839) : — 
If you place almonds in boiling water, and separate the testa, 
N N 2 
