6 MOSSES WITH A HAND-LENS 



is often as full of spring as if it were tempered steel, and the 

 little boxes are made with a lid which keeps everything snug until 

 the spores are ripe, when it falls and leaves the perforated cover, 

 which can open and close, open when dry and close when moist. 

 In damp weather it closes so that the spores may not be beaten 

 straight down by the rain or become wetted and spoiled inside 

 the capsule by a premature germination. This automatic per- 

 forated cover is in most cases composed of a fringe of teeth 

 around the mouth of the capsule ; these teeth close up when moist 

 and spread out when dry by a purely mechanical action which can 

 be performed long after the cells of the capsule are entirely lifeless. 



With the high power lens the teeth and cilia (see Peristome in 

 Glossary) can readily be seen in a dry capsule which is well pre- 

 served. 



In Georgia the capsules are erect, and its four teeth well 

 separated when dry, as seen in Fig. 3, PI. I. Dip one of the 

 dry capsules in warm water for a moment and see the peristome 

 close like a tiny vise, giving an almost comical impression of 

 grim determination. 



In Polytrichum the teeth are sixty-four in number, and of 

 themselves are usually so short that they would have little effect 

 on spor? distribution, but they are all attached by their tips to 

 the expanded membranous upper end of the columella, forming 

 a most effective and ingenious pepper-box, entirely automatic in 

 action. When the weather is dry, the teeth become shrunken in 

 width, and strongly incurved; the columella also shrinks, pulling 

 the ends of the teeth inwards (Fig. 2. PI. I) . This leaves ample 

 room for the spores to be shaken through the openings between the 

 teeth. The columella shrinks more at the margin than in the 



Explanation of Plate I. 



I. Moist peristome of Polytrichum Ohioense, R. & C. ^. The same 



dry. 3. Dry peristome of Georgia. 4. The same wet. 5. Four teeth 



of the peristome of Catharinea undulata (L.), Web. & Mohr. 6, 7, and 8 



represent different positions of the peristome of Barbula amplexa, I^esq.* 



7 shows the peristome immediately after the removal of the operculum. S 

 shows the appearance of the peristome of a dry capsule from which the 

 spores are escaping. The loosely twisted mesh of the narrow teeth forms 

 a perfect sieve to control the escape of the spores. If you place a per- 

 istome in this condition under the microscope without mounting medium 

 or cover-glass and breathe upon it the teeth will straighten perceptibly. If 

 you dip it in warm water it will assume the original position shown in 7, 

 if it be comparatively fresh; if it be rather old and somewhat broken it may- 

 look like 6. _ The perfect cone in 7 is, of course, a waterproof covering for 

 the spores inside. 



*As the peristomes were drawn by reflected light, the basal mem- 

 brane was scarcely noticeable. 



