TEXTBOOK OF BOTANY 



are growing (Fig. 53, A), and which withers when the spores 

 are ripe. 



Each spore sac (Fig. 53, B) has a slender stalk and a wall which is 

 composed of a layer of cells. The waU cells of one row, forming a 



Fig. S3. — A, a leaflet of the bracken fern, seen from below; the margin 

 is folded over so as to cover the spore sacs, which are borne near the edge. 

 B, a spore sac ; a, cells with specially thickened walls, which will bring 

 about the opening of the sac ; b, place at which the sac will open. 



partial ring that runs from the base of the sac up one side, over the 

 end, and part way down the other side, have very thick walls and 

 project beyond the neighboring cells. When the spores are ripe, this 

 ring of cells straightens suddenly, tearing the sac open and throwing 

 out the spores. 



The spores germinate in moist places, commonly on damp 

 soil. A spore develops at first into a row of cells, usually not 



Fig. 



B 



54- — ^, fern spores. B, C, early stages in the development of a 

 sexual plant from a spore ; o, wall of the spore ; b, rhizoids. 



