xx] 



RECENT FERNS 



303 



the form of finely divided leaves identified by earlier collectors as 

 those of a parasitic Trichomanes (fig. 235). In a letter written 

 by W. H. Harvey in 1837 accompanying the specimen shown 

 in fig. 235, he says, " Apropos of Hemitelia, be it known abroad 

 that supposed parasitical Trichomanes .. .is not a parasite, but 

 a part of the frond of Hemitelia." The delicate reduced pinnae 

 remain on the stem and form a cluster at the base of the 

 fronds ^. 



In many species the sporophylls are distinguished from the 



Fig. 234. Polypodium quercifolium. (Much reduced : M, Mantle-leaves.) 



sterile fronds by segments with little or no chlorophyllous tissue, 

 as in Onodea struthiopteris^ in which, each year, the plant pro- 

 duces a funnel-shaped group of sterile leaves followed later in 

 the season by a cluster of sporophylls; or, as in many other 

 genera, the fertile leaves are distinguished also by longer petioles 

 and thus serve as more efficient agents of spore-dissemination. 

 In Ceratopteris the narrow segments of the taller fertile leaves 



' A striking example of these so-called Aphlebiae of Hemitelia may be 

 seen at the Royal Gardens, Kew. 



2 Luerssen, in Babenhorst (89) A. p. 483, fig. 164. 



