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TEXTBOOK OF BOTANY 



whole under surface of the leaf. The sporangia are often grouped in dis- 

 tinct clusters known as sort ( sing, sorus ) . The sori may be located along 

 the veins, at the ends of veins, or along the margin of the leaf. The 

 shape, arrangement, and general appearance of the sori are commonly 

 used in distinguishing different genera and species of ferns. They are 

 usually covered by a delicate shield-like structure known as the in- 

 diisitim (Fig. 312). 



Fig. 312. Reproductive structures of a fern: A, section through part of a leaf 

 and a sorus composed of a stalked shield, or indusium, which covers a cluster 

 of sporangia in which numerous spores have developed; B, ventral surface of a 

 bisexual gametophyte; the antheridia are near the bases of the rhizoids, the 

 archegonia are just below the central sinus. B drawn by C. J. Chamberlain. Text- 

 book of Botany (Coulter, Barnes, and Cowles) , Amer. Bk. Co. 



Species such as the cinnamon fem and sensitive fern have two kinds 

 of leaves: the usual foliage leaf, and a smaller one on which sporangia 



