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A TEXTBOOK OF THEORETICAL BOTANY 



INNER 



PERISTOME 



TOOTH OF 

 ■^ OUTER 

 PERISTOME 



CELLS OF 

 — THE 



RING 



Fig. 410. — Mnium hornum. Section through the outer portion of the operculum showing 

 the development of the peristome teeth from the opposite walls of the peristome cells. 

 {After Strasburger.) 



Fig. 411. — Mnium hormim. Peristome. A, Teeth of outer peristome. 

 B, Teeth of inner peristome. {After Strasburger.) 



complex and is more closely adapted to a land habitat. The peristome in 

 particular, with its specialized mechanism for assuring that the spores shall 

 only be discharged in dry weather, is a highly elaborate structure, but we 

 shall find that analogous structures designed for regulating spore discharge 

 occur in other groups of land plants. 



Germination of the Spore 



When the spore reaches the ground it remains dormant until conditions 

 are favourable for germination, but in a damp environment the outer spore 

 coat soon splits open, and the inner wall swells outwards and develops into 

 the first cell. This cell elongates and divides, and from it is formed a series 



