^,o8 



SPOROPHYLLS 



thus used up to form four spores (Fig. 171, E). Their faces of 

 contact are more or less flattened and triangular, while the outer 

 walls are convex, so that each spore, at its inception, has the 

 form of a tetrahedron with a rounded base. In many cases, 

 however, the spores round off after the mother-cell membrane 

 has broken down. 



In most Ferns there is only one kind of frond which fulfils 

 the ordinary functions of a leaf, as well as those connected with 



Fig. 172. — The Hard Fern (Blechiuim spicant), showing foliage leaves and 

 sporophylls. [Photo E. J. S.] 



spore-production. In a few species, however, there is division 

 of labour, as in the Hard Fern (Blcchiium spicant, Fig. 172). 

 Here some of the leaves, spreading out near the surface of the 

 ground, have broad pinn;e and are purely vegetative, whilst 

 others, which assume an erect position, have narrow lobes and 

 are almost entirely concerned in the production of sporangia. 

 Such fertile leaves are called sporophylls. 



A less marked specialisation is seen in the Royal Fern 

 {Osmitnda regalis), where the lower part of tlie huge frond is 

 sterile, whilst the upper pinnules, bearing the sporangia on both 



