PROTONEMA 



287 



The peristome-teeth are extremely sensitive to changes in 

 the moisture-content of the air, curhng outwards when tire latter 

 is dry, and inwards when it is damp. In dry weather, therefore, 

 the powdery mass of spores inside the capsule is readilj' dispersed, 

 whilst in wet weather the dome is reconstituted (Fig. 156, E), 

 and the aperture, left by the shedding of the lid, closed. The 

 actual dispersal, in which the elasticitj' of the seta plays a 

 considerable part, is effected by a catapult-meclianism similar 

 to that of the Cowslip and Poppy fruits. 



Fig. 157. — Moss-protonema. A, Development of young Fimaria- plant (6.) 

 from the protonema (p.) (after Campbell). B, Stages in germination 

 of spores, and C, protonema of Dicranella heieromella (after Servettaz). 

 ^., gemma on protonema ; r., rhizoids ; sp., spore-membrane. D, Single 

 cell of overground part of protonema. 



The spores ultimately give rise to a new Liverwort or Moss, 

 but the adult plant is not produced directly on germination. 

 This is especially obvious in Mosses, where the spores in most 

 cases develop into a branched multicellular filamentous structure, 

 the protonema, which exists partly above and partly below 

 ground (Fig. 157, C). The overground portion appears as a 

 green weft on the surface of the soil, and its cells contain numerous 

 discoid chloroplasts (Fig. 157, D), whilst the underground portion 

 closely resembles the rhizoids of the ordinarj? Moss (Fig. 157, C, r.). 



