60 GENERAL REMARKS ON THE 



towards the margins of Avliich they must necessarily open : 

 hence, the characters of both genera not unfrequently occiu* 

 in the same frond, and are even exhibited by the same invo- 

 kicrum when it happens to extend below the origin of the 

 segm.ent. 



I have observed also, in the same place, that in Asplemiim 

 6S5] when the involucrum originates from the inner branch 

 of a primary vein, which is usually the case, it opens in- 

 wards or towards the mid-rib of the frond from which the 

 vein is derived ; and that when it arises from the lower or 

 outer branch of a vein it opens outwards, or in an opposite 

 direction, instances of which occur in several species of 

 the genus, in some of those especially where the frond is 

 simple. On the same law also depends the peculiar cha- 

 racter of Scolopendrium, in which the invokicra are pro- 

 duced in pairs, one of each pair originating from the lower 

 branch of a vein, the other from the upper branch of the 

 vein immediately below it ; they consequently open in oppo- 

 site directions and towards each other. This law, however, 

 in Asplenium is only observed where the vein has but few 

 branches, for when these are more numerous, and especially 

 when, in consequence of their greater number, the vein has 

 a manifest trunk or axis, the involucra of all its branches 

 open towards this axis ; the most remarkable instances of 

 this occur in those species of the genus which authors have 

 sepai'ated from it, under the name of Diplazium, where, 

 however, another peculiarity exists, depending on the same 

 law. This peculiarity consists in the inner branch of the 

 vein, or that adjoining the mid-rib, appearing to have a 

 relation not only to the axis of the vein but to that of the 

 pinna or frond from which the vein originates ; a relation 

 indicated by its having tAVO involucra, one of which bm-sts 

 towards the axis of the vein, the other towards the ad- 

 joining mid-rib. This double involucrum constitutes the 

 character of Diplazium, but as it is confined to the inner 

 branch, all the others being simple, and opening towards 

 the axis of the vein, there do not appear to be sufficient 

 grounds for its separation from Asplenium. I consider 

 the curved involucrum of Asplenium Filix-Fcsmina, Avhich 



