INTRODUCTION TO CRYPTOGAMIC BOTANY. 531 



anastomosing veins. LoxogramTua has an internal reticulated 

 venation, and sori produced on the elongated sides of the 

 areolae. The absence of costeeform veins and free veinlets 

 distinguishes it from Selliguea. Polytamia has several very- 

 long continuous sori between the rib and the margin, deeply 

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

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

 phyum, the sori, though reticulate, are sunk as in Polytcenia. 

 Diblemma is remarkable for having scattered sori in addition 

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

 mediate between the two sections, differing from GramrtiitidecB 

 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- 

 nogramma 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 costasform 

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

 Gymnogramma, are medial. Ceterach technically belongs to 

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

 the place of this is sujiplied 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 

 tril)e 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 Ceterach be excluded. 



601. Many of the species of Gymnogramma 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. 



u * 



