244 



VITTARIOID FERNS 



[CH. 



here numerous spicular cells are found. The sporangia are not restricted to 

 the veins, but are borne also upon the areolae, thus giving an Acrostichoid 

 character. On this account it was first named by Linnaeus Acrostichiun 

 citrifolhcm. 



The vascular system is variable: it appears as a very attenuated dictyo- 

 stele, with large leaf-gaps and perforations. Its most marked constituent is 

 a strong meristele which follows the lower side of the rhizome. A binary 

 leaf-trace supplies each leaf, the two strands arising near to the acroscopic 

 end of the leaf-gap: they fork early (Fig. 741,^). The sporangia, which are 



Fig. 744. AnetiiDii citrifolium (Kunze) Splitgerber. ^ = portion 

 of a frond, showing venation and sporangial distribution, with 

 peripheral spicular cells. ( x 4.) Z? = sporangium. (x200.) C= 

 group of small epidermal cells from which the sporangia arise. 

 ( X 200.) Z) = portion- of the lower epidermis, showing stomata, 

 a spicular cell, and glandular hairs. (After Williams.) 



small but of the usual type of the family, are short-stalked, with an annulus 

 of 12 to 14 indurated cells. They are borne in groups on special small-celled 

 patches, which spring by division of 3 or 4 cells of the epidermis. These 

 may lie either over the veins or on the surface of the intervening areolae 

 (Fig. 744). The spore-counts point to a typical number of 32 or 48. 



The prothalli of the three genera in which they are known are anomalous. 

 Those of Vittaria, Moiiogramine, and Hecistopteris have been accurately 

 described by Von Goebel (1888, 1896, 1924), and those of V. lineata by 

 Britton and Taylor (1902). The vegetative region is irregularly lobed, and 

 vegetative propagation by gemmae is similar to that already known in 



