— 55 — 



the teeth when wet curve inwards so strongly that the columella is pressed 

 against the mouth of the capsule, closing it effectually. Five minutes 

 study, however, will show any one that the teeth do not curve in when wet 

 but instead straighten up and outwards ; the columella also expands and 

 becomes of nearly the same diameter as the capsule. This makes the open- 

 ings lateral instead of terminal. The teeth expand enough laterally so that 

 not a single drop of water can enter or a spore escape. In addition the 

 spores seem to be protected by the nature of their outer surface, for it takes 

 a very long soaking to wet the spores so that they can be satisfactorily 

 mounted in water for microscopic study. 



In those species of Polytrichuin whose ripe capsules become horizontal or 

 pendent {P. commune, P. juniperinum, P. strictum, P. piliferujii) there is a 

 crest down the inner face of the teeth which bears cells which are free at 

 their outer ends, or these cells may be united to each other by their extremities. 

 Lindberg, who was the first to accurately describe these structures, compares 

 them to a minute stag's horn attached to the inner surface of each tooth. I 

 do not consider it proven that these crests are accessories developed to pre- 

 vent a too free delivery of spores in species with pendent capsules, but I do 

 consider the suggestion one worthy of serious consideration 



The peristome teeth of the Polytrichacaeae like those of Georgia have 

 none of the joints or articulations which are so conspicuous in the teeth of 

 most mosses. For this reason Mitten has united these two orders into a 

 group which he calls Nematodonte^ in contrast to the Arthrodonte^ or 

 jointed-toothed mosses. As in Georgia the teeth of the Hair-caps consist of 

 a solid mass of cells as is well shown in Fig. A, which shows a cross-sec- 

 tion of a tooth of Poly trie hu7J2 covimune. 

 These cells are very narrow, elongated, 

 and without transverse walls, these prob- 

 ably having been absorbed during the 

 earlier stages of development. These 

 cells thus form narrow elongated fibres 

 passing up one side of the tooth, forming 

 an arch and then passing down the other 

 side, across through the basal membrane 

 to the next tooth and then up that and so 

 on. If one were to take a pen and trace a 

 continuous line around the edges of the 

 Fig. A. Cross section of a tooth teeth in PI. 5, Fig 5. it would well represent 

 of Poly trie hiii7i commune. the course of these fibrous cells which are 

 illustrated in cross section in our figure. These lines can be easily seen by 

 examining the peristome under the compound microscope. The continuous 

 fibres are best seen near the edge of the tooth. 



Plate 5, Figs. 6, 7 and 8 represent different positions of the peristome of 

 Barbula amplexa Lesq.* As the peristomes were drawn by reflected light the 

 basal membrane was scarcely noticeable. Fig. 7 shows the peristome im- 

 mediately after the removal of the operculum. Fig. 8 shows the ap- 



*As the peristomes were drawn by reflected light, the basal membrane was scarcely- 

 noticeable. 



