195 



Hal). Mexico, near Mirador, Schaffner, n. 152. — The author offers no comiia- 

 rison between this and any other Pteris ; I am therefore ignorant of its affinities. 

 He only further adds that " it is a species very remarkable for the blood-red- 

 coloured petioles, the caudiform appendage which terminates the pinnides, and 

 for the distant nervils." 



{Involucre double ! inner one sometimes obsolete. Fronds coriaceous, 3~i-pinnate, 

 erect or scandent ; margin of the pinnules stronyly recurved, Caudex ijuite 

 subterraneous, very long, creeping. Fronds distant on the caudex. — Pteris, 

 § Ornithopteris, Ag.; § Aciuilinoptkride.e, Gaud. Allosorus, § Aaui- 

 i.iNi, Pr. — Easily as the outer involucre of the Pteris aquilina is to l)e seen, 

 even with the naked eye, the inner one, except in a peculiar state of tlie soriis 

 (before it is mature), can only be brought to view by careful dissection under 

 the microscope.* I have however satisfied myself of its existence, though I 

 have often failed to detect it : indeed the fact appears to be ignored by the 



* Its presence was detected by the late Thomas Smith, Esq., of the Temple, 

 London, and communicated to me in 1819, in a letter which I published in the 

 ' Flora Scotica,' and which deserves here to be recorded. He considered this inner 

 involucre (I scarcely know upon what grounds) to be the real involucre. " It 

 will be found," he says, " exactly opposite to that which is seen on the edge of 

 the frond, and, between the two, the line of capsules is placed. It may be called 

 the inner involucre, and much resembles the outer, having, like that, a ciliated 

 edge ; but, instead of being flat, it curls inwards, covering the capsules in their 

 young state, and being itself covered by the outer one. It is best, perhaps, seen 

 when the capsules are about half ripe, at which time it is nearly the same breadth 

 as the outer one, and is readily seen by the assistance of the microscope. In tex- 

 ture it seems to differ a little from the outer." 



" According to the principles upon which genera are formed in this Order, the 

 inner involucrum appears to afford a character which would justify the forming a 

 new genus. I have found it in Pt. caudata, which is very nearly allied to aqui- 

 lina ; it also occurs in Pt. esculenta, and our mutual friend Brown authorizes me 

 to say that it is found in a small group of the genus Pteris, the species of which 

 agree in habit, and are mostly extratropical, differing from the tropical species in 

 having a thicker and harder frond, and not a thin filmy one, which exists in most 

 of the latter. It is perhaps not unworthy of remark that this involucrum is never 

 seen, except when there is fructification. The outer one, it is well known, is 

 almost always present, whether there is fructification or not, a circumstance, I 

 believe, which does not generally take place in a true involucrum."— 5»2i7A, in 

 Letter, Aug. 1819. 



Since the above was sent to press, I have been favoured by my friend Mr. 

 Wilson, of Warrington, with excellent magnified drawings of the double involucre 

 both of Pt. (Ornithopteris) aquilina and scalaris, which will occupy Tab. CXLI. 

 (the first plate of our Vol. III.), for they show the nature and structure l)etter 

 than any description of mine can do. I may add here however the following 

 observations of Mr. Wilson : — " The interior (true ?) involucre of Pt. scalaris is 

 thrice as broad as that of Pt. aquilina, and is the more conspicuous from the nar- 

 rowness of the marginal cover, and the absence of the fringe of ciliary processes ; 

 but if smaller in Pt. aquilina, it is almost as easily found, from its being coloured. 

 I do not find any interior involucre in the American forms of Pt. aquilina, but as 

 it docs occur, though not constantly, in Pt. esculenta, Forster, I may on a future 

 attempt find some traces even in them." — He has since found the inner cover to 

 exist in several forms of the N. American Pt. aquilina, even in specimens on 

 which he had not succeeded in detecting it before ; " sometimes being obvious 

 r'noiigb in one part, and in another quite obsolete." 



