The President's Address. By Dr. R. Braithwaite. 141 
spherical, pyriform, oblong, cylindric or angular, and it may be erect, 
drooping, or pendulous ; the surface has an epidermal layer of flat, 
empty cells, generally perforated by stomata, by which a communica- 
tion is maintained between the atmosphere and the interior of the 
capsule. The stomata have two guard-cells, and resemble those on 
the leaves of flowering plants ; they are either superficial, when on 
the level of the epidermis ; or immersed when below the level of the 
epidermis, and more or less covered by its cells ; the capsules of 
Funaria, Splachnum, Mnium, Orthotrichum , &c., present examples. 
A flask-like or umbrella-shaped swelling — the hypophysis — is some- 
times present between the seta and capsule, very distinct in the genus 
Splachnum. 
On transverse section of a fully formed theca we see that it is com- 
posed of (1) the capsule wall, (2) an internal air-cavity, (3) the spore- 
sac with its sporogenous layer, (4) the columella. The spore-sac is 
generally closely applied to the columella, but in Polytrichum an 
intercellular space separates them. For extremely beautiful figures 
of sections of capsules I may mention the paper of Lantzius-Beninga, 
‘ Beitrage zur Kenntn. der ausgew. Mooskapsel.’ The lower part of 
the capsule tapers down into the seta by its neck, the upper end being 
closed by an operculum or lid, flat, conical, or with a long beak, which 
is, however, wanting in Andresea, and a number of the smallest 
mosses differing much in habit, which have been grouped together 
under the term Cleistocarpi, but are more naturally arranged as the 
lowest forms of families having a similar leaf-structure ( Phascum , 
Ephemerum, Acaulon , Physcomitrella , &c.). Between the stoma or 
capsule mouth and the lid is often found an annulus or ring, com- 
posed of one or more rows of large empty cells, flattened, thin- walled, 
and highly hygroscopic, and by their swelling the lid is lifted off ; the 
outer wall of each of its cells is thickened and does not expand, and 
thus the annulus often breaks and rolls back as a spiral band. 
When the lid is detached that beautiful appendage of the capsule, 
the peristome, comes into view ; in Georgia it is represented by four 
pyramidal masses composed principally of the material of the lid ; in 
the Polytrichacese it consists of 16, 32, or 64 non-articulate processes 
composed of bundles of fine-thickened fibres cemented together by 
cellular tissue, and bound down at their points to the margin of the 
epiphragm or dilated apex of the columella, which is left as a layer of 
cells covering the mouth. In the exotic genus Dawsonia these 
filaments are free and project from the mouth of the capsule like a 
brush. In most mosses, however, the teeth are formed of thickened 
plates — only in Splachnum do they consist of true cells — and the 
transverse and longitudinal lines on the outer surface show the divid- 
ing lines of constituent cells. In Seligeria and Orthotrichum the 
teeth are unistratose, but in most other masses bistratose ; the two 
sides of the teeth are differently hygroscopic, and thus they curve by 
change of moisture. M. Philibert has written a series of valuable 
