MOSSES AND LIVERWORTS (BRYOPHYTES) 263 



mosses use this number as the basis of distinguishing one 

 species from another. On account of the regular thickenings 

 upon the teeth they are readily affected by moisture changes ; 

 that is, they are hygroscopic. When they extend within the 

 capsule the spores adhere to them. As they straighten and 

 extend outward they move with a jerking motion which serves 

 to throw the spores about. A moss may be made to repeat the 

 characteristic tooth movements under a hand lens or low power 

 of a microscope, by being moistened and then fanned until dry. 



The spores developed within the 

 capsules are made entirely by cell 

 division and are therefore asexual 

 spores. As seen in 

 Section 242, they 

 may germinate and 

 produce protonema. 

 Because of the large 

 number and wide 

 distribution of asex- 

 ual spores, abun- 

 dant production of FlG - 22 - Ti P s of moss capsules 



protonema OCCUrS -^ a s ^ e v * ew ' a m oss capsule showing the teeth (t) , 



, f , and the mouth or peristome (p) , to which the teeth 



When the lavorable are attached. (Considerably enlarged.) B, an end 



Conditions of mois- view of a moss capsule. Note the peculiar spiral 



. , , arrangement of the teeth and the transverse thicken- 



ture, light, and tem- j ngs upon them . (Greatly enlarged) 



perature exist. 



246. The moss plant : alternate stages in the life cycle. It 

 is evident that in the mosses sexual and asexual reproduction 

 are limited, each to a distinct part of the life cycle. It is also 

 evident that each of these parts of the life cycle forms a kind 

 of spore which, upon germination, produces not the same part 

 of the life cycle, but the other part. The asexual spore that is 

 formed in the capsule germinates and produces protonema, 

 which, by means of buds, produces the leafy plant; the oospore, 

 which is produced by union of gametes, the egg and sperm, 

 germinates and produces the foot, seta, and capsule. The 



