FILICES. 



125 



The first of Milde's subspecies "nigrum," Heufler, contains _ the 

 forms here called genuinum and obiusatum. It is the least divided 

 of the three, and has usually the stipes not exceeding the lamina, 

 which is usually about 6 or 8* inches long, by 2 to 3 inches across the 

 broadest part at the base ; the frond is coriaceous and opaque with 

 a greasy lustre, the ultimate segments are convex on the outer side. 

 Milde's var. obtusatum is a less developed form, with the stipes usually 

 shorter in proportion to the frond, which is rarely above 4 inches in 

 length, and sometimes as little as 2 inches ; it is less divided, and 

 sometimes scarcely bipinnate ; the ultimate segments are rounder and 

 more obtuse than in var. genuinum, into which it passes insensibly, and 

 is scarcely worthy of the name of a variety. Milde gives as one of 

 the characters of his first form that there is only a solitary vascular 

 bundle in the stipes, while in the second subspecies there are 1 or 2 

 bundles, and in the third two. I fear little reliance can be placed 

 upon this character ; in all the specimens I have examined there are 

 two vascular bundles in the stipes where it starts from the caudex. 

 These two bundles approach each other and coalesce before reaching 

 the lamina. In small specimens the coalescence occurs much nearer 

 the base than in large ones, but the point at which it does occur 

 appears to depend on the degree to which the stipes is developed. 

 Speaking of the petiole of Asplenium Adiantum-nigrum, Mons. Duval 

 Jouve says : " A leur base dilate'e ils pre'sentent de_ chaque cote et 

 presque contre la peripheric un faisceau fibro-vasculaire simple, dont 

 la coupe est re'niforme oblique; plus haut, ces deux faisceaux se 

 rapprochent vers le centre sans jamais se fondre en un seul " (Billot, 

 Annot. Fl. de Fr. et d'All.' p. 247). My experience is contrary to 

 this, as I find the two bundles always ultimately coalesce, and some- 

 times indeed very near the base ; so I suspect the unity or duality 

 of the vascular bundles varies in different specimens. 



The second subspecies, " Serpentini," Tausch., appears to be confined 

 to serpentine rocks in Saxony and Silesia, south to Italy, Dalmatia, and 

 Hungary. It was first recorded as a British plant by Mr. T. Moore, 

 from specimens collected by the Rev. A. Christie, on serpentine rocks 

 at Cabrach, Aberdeenshire. It differs from the commoner form of 

 Adiantum-nigrum by its lamina being more divided, and the ultimate 

 segments less approximate, and more or less bent away from the 

 partial rachis. The frond also is dim, without the greasy lustre of 

 the common form, or the satiny lustre of the form acutum. _ Milde 

 says concerning it, that he has often found fronds passing into A. 

 Adiantum-nigrum on the same rhizome with A. Serpentini. The 

 stipes is usually longer than the frond, often conspicuously so. 

 The lamina is from 4 to 6 inches long in the specimens I have seen. 

 Milde says the fronds do not last through the winter, but in answer 

 to a query of mine on this point, Mr. Christie writes that the 

 fronds are evergreen at Cabrach. Along with the true Serpentini 

 there grows a form connecting it with ordinary Adiantum-nigrum. 



