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TEXTBOOK OF BOTANY 



that the upper, broader end of the spore sac is turned downward. This 

 upper end forms a lid which drops off when the spores are ripe. But 

 the falling of the lid does not leave entirely uncovered the cavity in 

 which the spores lie ; for attached to the margin of this cavity are 

 two circles of teeth (Fig. 46, C). 



In moist weather the teeth bend inward, closing the mouth of the 

 cavity and so preventing the escape of the spores as well as the entrance 

 of water into the spore sac. In dry weather the teeth curve outward, 

 and through the open spaces between them the spores may sift out. 

 Because of the presence of the teeth and of their changes in position, 

 the spores are scattered a few at a time ; thus, the chances are increased 

 that some spores at least will land in a convenient place and under 

 conditions favorable for germination. The spores are much like those 

 of fungi excepting that they contain chloroplasts. 



121. The Protonema. — A moss spore, falling upon moist 

 soil or upon a moist stone, brick, or piece of wood, germinates 



by pushing out 

 a projection that 

 grows in length 

 and is soon di- 

 vided by a cross 

 wall. As the 

 young plant con- 

 tinues to grow, 

 more cross walls 

 are formed ; the 

 plant now con- 

 sists of a row of 

 cells arranged 

 end to end (Fig. 

 47, B). A sec- 

 ond projection 

 often grows out 

 from the oppo- 

 site side of the 

 spore and develops into a part of the same plant. The plant 

 branches freely and looks much like a branching green alga 



Fig. 47. — A, spores of Funaria. B, a young plant 

 developed from a germinating spore ; this plant grows 

 into the protonema (C) ; 6, a bud of the protonema 

 which will develop into an upright leafy branch (or 

 "moss plant"). 



