34 



DAVALLIOID FERNS 



[CH. 



stalk, and frequently the series of its cells is interrupted there (Fig. 604). 

 The number of spores in the sporangium is lo\y, viz. 24 to 32, an indication 

 of advance. 



Fig. 604, i — iv. Sporangia of Lindsaya linearis, seen from various 

 points of view, showing the incomplete annuhis. ( x 125.) 



DICTYOXIPHIUM Hooker 



Such types as Lindsaya sagittata or reniforme give the nearest points of 

 comparison with the rare and peculiar fern, D. panamense Hk., figured by 

 Sir W. Hooker {Gen. Fil. Plate LXIl), and compared by him with Lindsaya. 

 Here the coenosori extend along both margins of the entire and reticulate 

 leaf-blade, with a vascular commissure traversing each receptacle. A special 

 peculiarity lies in the absence of the upper or adaxial indusium: but the 

 abaxial is present, and the receptacle 

 is tilted towards the upper surface, over 

 which its mixed mass of sporangia may 



beslightlyextended(Fig.605).Pending pjg. g^^. Transverse section of a sporophyll of 

 more detailed examination of this rare Dntyoxiphium panamense Hk. with the adaxial 

 . . surface directed upwards, (x 18.) 



fern, it may be held provisionally to 



be an end term of the coenosoric Lindsayas, but here while the receptacle is 



marginal, the upper indusium is abortive, and the numerous sporangia are of 



mixed origin. The three-rowed sporangial stalk corresponds to that seen in 



Lindsaya. 



Unfortunately these comparisons of Davallioid Ferns are necessarily based 

 upon the features of the sporophyte. There is as yet no sufficient knowledge 

 of the details of the gametophyte in these ferns, so often rare and local. But 

 there is no reason yet apparent for thinking that the facts when acquired 

 will be subversive of the conclusions based upon the richer and more depend- 

 able data drawn from the sporophyte. 



