PTERIDOPHYTA 



279 



multiplication of the gametophyte, independently of the spores. The sexual 

 organs are similar to those of the Osmundacese. 



Sporophyte. The sporophyte of the Hymenophyllaceae is usually small, and 

 is characterized by the extreme delicacy of the leaves. The slender, creeping 

 stem is monostelic, and roots are often quite absent. Where they are present they 

 are much like those of the typical Ferns, but show much variation in the num- 

 ber of xylem-masses. The plants are very generally epiphytes, or grow upon 

 rocks exposed to the spray of mountain streams or cataracts. The adaptation to an 

 excessively moist atmosphere is seen in the leaves, which, with few exceptions, 



T"iG. 246. Ciboti.um Menziesii. A, pinnule with sori, s (X 3). B, sorus, with two- 

 valved indusium (X 9). C, sporangium (x 80). D, paraphysis (X 80). 



consist of a single layer only of green cells stretched between the veins. This 

 gives the leaf the filmy texture of a Moss-leaf, and is the reason for their name. 



Sporangium. The sporangia (Fig. 245) are borne at the ends of the veins 

 upon a receptacle which in Trichomanes becomes extremely elongated. The 

 sorus is surrounded by a tubular or bilobed indusium. The sporangium has a 

 broad, oblique annulus. The tetrahedral spores at maturity contain chlorophyll. 



Family 6. Cyatheaceae 



The Cyatheacese are Tree-ferns which structurally closely resem- 

 ble the Polypodiaceae, from which they differ mainly in the oblique 

 annulus of the sporangium and the cup-shaped indusium (Fig. 246). 



