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BOTANY: PRINCIPLES AND PROBLEMS 



Fig. 199. — The structure of a fern (Aspidium). A, the. plant as a whole. 

 B, portion of leaf with seven fruiting dots or sori on its lower surface. Each is 

 covered by an indusium (a), from under which the sporangia (6) are protruding, 

 in one case. C, a single sporangium. D, transverse section through a sorus, 

 showing section of leaf-blade above and of indusium below, with cluster of 

 sporangia attached between them. {From Strasburger, after Wossidlo). 



