. The Bryologist. Mosses; Liverworts; Lichens; Botany; Bryology. -63- THE PERISTOHE V. By a. J. Grout. In my third article on this topic I called attention to the fact that the peristomes of the Buxbaumiaceae are somewhat intermediate between the Arthrodont and Nematodont types. In the Encalyptaceae also there are some interesting transitional stages which, perhaps, will be better under- stood after we consider the method of formation of the Arthrodont peristome in detail. I have chosen Mfimm hoi-num to illustrate this article because Schimper's illustrations of this species serves my purpose
. The Bryologist. Mosses; Liverworts; Lichens; Botany; Bryology. -63- THE PERISTOHE V. By a. J. Grout. In my third article on this topic I called attention to the fact that the peristomes of the Buxbaumiaceae are somewhat intermediate between the Arthrodont and Nematodont types. In the Encalyptaceae also there are some interesting transitional stages which, perhaps, will be better under- stood after we consider the method of formation of the Arthrodont peristome in detail. I have chosen Mfimm hoi-num to illustrate this article because Schimper's illustrations of this species serves my purpose so well. Fig. I. Transverse section through the upper part of a nearly ripe mature capsule of Mnitim hornum. This figure shows th^ upper portion of the archesporium with several spores: the columella occupies the upper portion inside the peristome; the annulus is shown at the junction of the operculum with the mouth of the capsule; x 120. The basis of the Arthrodont peristome, both double (Dipio- lepideae) and single (Aplolepidese) is a layer of sixteen large cells lying just underneath the oper- culum and shown in cross section in Fig. 3. This layer we will call the peristomial layer for conveni- ence. In Mnium hormcvi and nearly all the double peristomed Fig. I. mosses except the Funariaceae the teeth of the outer peristome are formed by the thickening of the outer walls of the cells, and the inner peristome by a much less pronounced thick- ening of the inner walls. The thickening laid down on the outer walls is continued along the horizontal walls which separate each tier of cells, form- the projection (trabeculae) on the inner faces or the teeth, Fig. 5 and Fig. 2, b. These trabeculae and the walls thus thickened form the transverse lines separating the joints or articulations in the teeth of Mnium, Bryum, Hyp- 711(711, etc. The layer of cells next outside the peristomial layer is composed of twice as many cells, and the median ziz-zag line of the peristome teeth marks the
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