INTRODUCTION TO CRYPTOGAMIC BOTANY. 531 



anastomosing veins. Loocogramma has an internal reticulated 

 venation, and sori produced on the elongated sides of the 

 areolse. The absence of costseform veins and free veinlets 

 distinguishes it from Selliguea. Folytcenia has several very- 

 long continuous sori between the rib and the margin, deeply 

 imniersed, and seated on the longitudinal veins. The frond is, 

 as it were, pinched up on either side of the sori.* In Antro- 

 phyum, the sori, though reticulate, are sunk as in Polytc&nia. 

 DibleTnma is remarkable for having scattered sori in addition 

 to the marginal, with reticulated venation. Selliguea is inter- 

 mediate between the two sections, differing from GrairnmitidecB 

 in having linear sori seated between the nerves. , It bears the 

 same relation to them that Fhymatodes does to Polypodiacece. 



600. We come now to the allies of Hemionitis. In Gym- 

 nogra^mma the sori are on the forked veins or veinlets, and 

 at length frequently become confluent. In Hemionitis the 

 veins are much branched and reticulated, and to a great 

 extent occupied by sori. In Leptogramma we have costseform 

 pinnate veins, with free parallel veinlets. The sori, as in 

 Gymnogramma, are medial. Geterach technically belongs to 

 this tribe, in consequence of the absence of an indusium, but 

 the place of this is supplied by the abundant scales, and its 

 affinities seem to be rather with Asplenium, to which it is 

 very closely related, than with Grammitis. This is one of the 

 instances in which the presence or absence of an indusium 

 must not be taken as decisive of affinity. Though this tribe 

 contains many tropical and subtropical forms, we have a sprink- 

 ling of more temperate species. Both the New Zealand species 

 of Gymnogramma occur in Europe, and other species of the 

 tribe occur in Madeira. They do not, however, extend far 

 north. None appear in the Flora of the Northern United 

 States, nor in Great Britain, if Geterach be excluded. 



601. Many of the species of Gymnogram'ma are remarkable 

 for the white or variously tinted yellow meal with which the 

 under side is clothed. As many varieties combining the cha- 



* It is to be observed that in Vittaria the sori are sunk in a marginal 

 groove, and in Pteropsis at a little distance from the margin. Here 

 they are not single. 

 34 * 



