XLV] CHRISTOPTERIS 213 



facts accord with the relatively primitive origin ascribed to Platy cerium, but 

 they do not bring any very distinctive material for further comparison. 



CHRISTOPTERIS TRICUSPIS Christ 



This fine Fern was first described, from Sikkim specimens, in Hooker's 

 Species Filicum, Vol. V, p. 272, PI. CCCIV, as Acrostic/mm {Gyninopteris) 

 triciispe Hooker: it stands in Christ's Farjikrdiiter, p. 49, and in Natilrl. 

 Pflansenfam. 4, I, p. 199, as Gyninopteris tricuspis (Hook.) Bedd. : but it finds 

 its best place in Copeland's genus Christopteris {Philipp. Journ. Botany, 

 Vol. XII, 6, 19 1 7). There has never been any doubt as to its identity, nor as 

 to its close relation with Cheiropleuria. Describing it in 1864 Sir William 

 Hooker writes: "This very fine and new species, with not a little of the 

 habit and venulation of A. bicnspe, differs remarkably in being trilobed or 

 tripartite, and it has always a solitary central cos'ta to each lobe. One of my 

 specimens has the three segments only partially contracted and fertile." 



The photographic Figure 722 shows the habit of this upstanding, ground- 

 growing species, which may attain some three feet in height. The petioles 

 rising from the creeping rhizome are doubtless elongated, as in Dipteris and 

 Cheiropleuria, in relation to the herbage amongst which it grows. At its base 

 the leaf-stalk enlarges into a mammillary swelling, which persists with a 

 terminal scar marking a smooth abscission. There is occasional branching 

 of the flieshy axis, but it is independent of the leaf-bases, as it is also in 

 Dipteris. The rhizome is covered by brown scales, which fall away with age. 



The leaves are strongly dimorphic, though sometimes only half fertile, the 

 soriferous part being then contracted, as in Hymenolepis (Syn. Fil. p. 422). 

 The ternate form of the blade with a large terminal lobe appears at first 

 sight far removed from the dichotomy prevalent in Dipteroid Ferns: 

 occasionally more than three lobes may appear (see Frontispiece). But a 

 reference to Vol. I, Chapter V, and particularly to Figs, 'jj and 80, will show 

 how nearly related in origin a ternate, and even a more richly lobed 

 leaf, may be to equal dichotomy. In this, as in its dermal scales and other 

 features to be described later, C. tj'icuspis is in advance of Cheiropleuria: 

 nevertheless, the more detailed examination of to-day will be found to 

 confirm the original forecast of Sir W. Hooker. 



The rather fleshy axis, which is about \ inch in diameter, is traversed by 

 a cylindrical, highly perforated dictyostele, which presents in transverse 

 section a ring of some 12 small meristeles. When a leaf-trace departs, some 

 five of these arch outwards and pass into the petiole, the two marginal 

 being the largest, with the usual hooked x)-lems. After this the ring again 

 closes. The whole construction is such as would naturally follow if a 

 solenostele, giving off a leaf-trace such as that seen in Dipteris or Metaxya, 



