220 



GENERAL BIOLOGY 



These spore-mother cells are divided twice, thus producing four 

 spores each, and it is these spores which eventually germinate and pro- 

 duce the gametophytes. In ferns, we shall see that a quite similar 

 process of spore formation takes place. 



'During the time the spores are maturing, a circular groove, called 

 an annulus, forms near the apex of the spore-case. The cells in this 

 region have thinner walls than the surrounding cells. These cells later 



become dry, and the thinnest part becomes torn 

 to form a lid or operculum ( ) 



at the summit of the spore-case. As the opercu- 

 lum falls away, the sperm are dispersed. 



If they find suitable soil a short green proto- 

 nema (Fig. 116) germinates The tip of the 

 protonema broadens to form the prothallus 

 w r hich is one cell in thickness. Tiny rhizoids 

 ( ) form on the under 



side and from the margin, while other threads 

 c o n t a i n i ng chlorophyl 

 then develop. Often a 

 thallus forms at the tip of 

 each of these threads. 

 From this thallus a leafy 

 branch grows upward and 

 the sphagnum plant de- 

 scribed is again a full- 

 fledged adult organism. 

 The plant, from the time 

 it germinates from the 



Fig. 117. 



Sphagnum Cuspidatum, 

 showing innovation, or 

 short, branches. ( After 

 Schimper.) 



Fig. 118. I. 

 The Sporophyte of a Common Moss (Funaria). 



A., young sporophyte s. attached to the leafy moss 

 plant and covered by the calyptra cat. B., sporophyte 

 with mature spore case sc. and calyptra cal. at the 

 tip. C., spore case with calyptra removed ; o., the 

 cover (operculum). D., a stoma from the surface of 

 the spore case. E., section of young spore case, show- 

 ing the cylindrical central region of spore-producing 

 tissue sp. F., the spore-producing tissue in detail. 

 (From Bergen & Davis "Principles of Botany," by 

 permission of Ginn & Co., Publishers.) 



Fig. 118. II Developing Sporophytes 

 of a Common Moss (Funaria). 

 A, very young stage, showing the 

 early cell divisions of the egg ; /?., 

 older sporophyte just before the 

 archegonium o. is torn away from 

 the gametophyte and carried up- 

 ward as the calyptra. The base of 

 the sporophyte has now grown down 

 into the tip of the leafy moss plant 

 (gametophyte) and is firmly an- 

 chored to it. (After Sachs.) 



