DIMORPHISM OF FERNS. 



341 



ferns are examples of this interesting relation between the leaves 

 like the common sensitive fern (Onoclea sensibilis) and the 

 ostrich fern (O. struthiopteris) and the cinnamon fern (Osmunda 

 cinnamomea). The sensitive fern is here shown in fig. 445. 

 The sterile leaves are large, broadly expanded, and pinnate, the 



Fig. 445- 

 Sensitive fern ; normal condition of vegetative leaves and sporophylls. 



pinnae being quite large. The fertile leaves are shown also in 

 the figure, and at first one would not take them for leaves at all. 

 But if we examine them carefully we see that the general plan 

 of the leaf is the same : the two rows of pinnae which are here 

 much shorter than in the sterile leaf, and the pinnules, or smaller 



