196 Plant Biology 



spore-producing, green leaves are called sporophylls (Fig. 68). All the 

 common ferns produce one type of spore and are therefore homosporous. 

 When sporangia are grouped in clusters, they are known as sori (Gr. 

 soros, heap). Each sporangium consists of a capsule borne on a stalk. 



Fig. 68. — Fruiting fronds of various ferns showing the ways in which spores 

 are produced. 1, Sensitive fern; 2, cinnamon fern; 3, climbing fern; 4, common 

 grape fern; 5, common polypody fern (Poly podium) ; 6, bracken fern (Pteridium) ; 

 7 , maiden hair fern; S, common chain fern; 9, Christmas fern; 10, spinulose shield 

 fern; //;, common bladder fern; 12, obtuse woodsia fern; 13, boulder fern; 

 14, walking fern; 15, ebony spleenwort fern. (Copyright by General Biological 

 Supply House, Inc., Chicago.) 



The capsule wall contains a row of special, moisture-sensitive cells known 

 as the annulus (an' u lus) (L. annulus, ring). The walls of the annulus 

 cells are thicker on one side and, when affected by moisture, tend to 

 straighten the annulus, thus throwing the spores from the ruptured 

 capsule. 



