DISTRIBUTION' OF SPORES AND SEEDS. 355 



stalk, so that it is surrounded by a mass of mucilage, thus 

 enabling it to adhere to any object which it strikes. 



Filaments carrying the spores often twist upon drying 

 and thus jerk off the spores as they suddenly slip past some 

 obstruction. When spores are produced in chains, either 

 the walls of a special cell or a layer of the cell-wall between 

 them may act as a separator by its alteration into mucilage 

 (A, fig. 399). In some cases the spores are wedged apart by 

 the secretion, between the layers of the wall joining them, of 

 a cellulose plug which gradually elongates into a slender 

 spindle to whose tips the spores are so slightly attached that 

 the lightest breath carries them away (.5*, fig. 399). The 

 elaters of the liverworts (fig. n and ^[ 321) serve in some 

 cases to sling out the spores when the capsule bursts ; in other 

 cases, as in Marchantia, they entangle the spores, insuring 

 gradual and preventing too sparing distribution. The teeth 

 around the mouth of the capsule of mosses serve to distribute 

 the spores at opportune intervals, instead of having them 

 emptied out all at once. In some mosses the teeth are erect 

 or recurved when dry, but upon being moistened they arch 

 over the mouth, thus 

 forming a nearly closed 

 cover (fig. 400). Others 

 have the teeth arched 

 over the mouth when 

 dry or permanently fas- 

 tened together by their 

 tips, thus narrowing the 

 opening and allowing 



i . c 



the Spores tO Sift Ollt FlG 400> _ L - apsu i cs of a moss ;,-//) after 



liPfwppn tl-ipm T n cnmp fal1 of lid - -Meeth erect when dry, leaving cap- 

 11 sule widely open ; /A the same in damp weather. 



cases the teeth, by their 



form and hygroscopic curvatures, serve to sling out the spores 



to a short distance. In many ferns the annulus of the spo- 



