Mr. VALENTINE on the existence of Stomata in Mosses. 241 
tracting so as to close this cavity, fig. 1. and fig. 2., thereby forming an addi- 
tional impediment to evaporation or respiration, as the case may be. The 
nearest approach to this structure is in Marchantia and Targionia, in which 
the stomata are formed of several layers of cells, one above the other, and con- 
tracting upwards so as to produce a hollow truncated cone. 
The obturator ring described by Mirbel does not exist, as was ascertained 
by Griffith to be the case with Targionia hypophylla, but instead there is a 
quantity of short perpendicular filaments, which project into and form the 
floor of the cavity of the stoma, and are seated on a dense mass of roundish 
cells which contain a great quantity of green granules. "The species of Mar- 
chantia which was the subject of Mirbel's observations is not mentioned in 
Lindley's Botany, one of the tracts published by the Society for the Diffusion 
of Useful Knowledge; and as my knowledge of this subject is obtained from 
a second source, you cannot expect it to be so clear as it would have been if 
I had had the original memoir to consult. If Mirbel describes the obturator 
ring as common to all the species, he is wrong; but it is more probable that 
his remarks apply to polymorpha, the most common species, and as that is not 
immediately within my reach, J cannot either confirm or contradict him. 
There is this important peculiarity in the stomata of Marchantia conica—it 
has not the power of contracting after having been once pervious. 
Tas. XXI. fig. 6, 7, 8, and 9 represent the stomata of Funaria hygrometrica, 
each of which consists of a single cell in the form of a hollow ring, the sides 
being so compressed as to convert the aperture into a mere slit. They only 
occur on the apophysis, which is composed of very loose cellular tissue (except- 
ing its centre), and through the intercellular spaces of this tissue they allow of 
a communication between the external air and the space between the sporular 
and thecal membranes. In Orthotrichum diaphanum the stomata open directly 
into this space, and I believe, although I have not been able to prove it, that 
in all mosses the stomata communicate with this space. All the cells exposed 
to the action of the air contain green granules; and some, as those forming 
the external layer of the columella, which have no apparent communication 
with the air, also contain them, although in a less degree, and occasionally a 
few granules are scattered in the cells which form the substance of the colu- 
mella, as shown in fig. 1.; the more retired, however, the cells are from the 
