THE STRUCTURE OF FERNS 



331 



tion that the fern is a much larger and more efficient plant 

 than the moss. It has large leaves and an ample root 

 system. By cutting sections of these organs and of the 

 stems a corresponding complexity and efficiency of organ- 

 ization is revealed in their inner structure. The spores, 

 with which we are chiefly concerned, are commonly pro- 

 duced on the backs of the leaves. The accompanying 



Fig. 85. — The Sporophyte or sexual plant of the fern. 1. a whole 

 plant showing (a) the stem, (6) the roots, and (c) the leaves. 2. the 

 back of a leaflet showing clusters of sporangia and the branched 

 "veins" through which water and dissolved food are transported. 

 3, a section through a cluster of sporangia on a different sort of fern 

 with a flap -like cover or indusium. 4. a single sporangium showing 

 the stalk and the ring-like "annulus" around the rim, made of 

 thickened cells, whose function is to open the sporangium and dis- 

 charge the ripe spores through the mouth-like opening at the left. 

 5. a cross section of the stem showing two dark bands of strong 

 stiffening tissue and several round or oval bundles of conducting 

 tissues. 



illustrations show various details of spore production. At 

 present we are concerned only with the facts that the 

 spores are all alike and that they fall on moist soil, where 



