78 



POLYPODIACEiE. 



[ACROGENa. 



Order XXIV. POL YPODIACEJE.— Ferns. 





to "be of no greater importance than 

 purposes of classification. The order c 

 •^■o&" l ,:u ' t °f s P eeies bearing their spore-cas 



leaves, usually named fronds ; with tr 



^&?<3 



QrnUe, Swart: BmoptU Filicum, (1806).— Filices vera-, Willd. Sp. PL 5. 99. (1810.)— Polypodiaceie, 

 R Brown Prodr. 145. (1810); Agardh A ph. 116. (1822) ; Kaulfutt Enumeratio, 55. (1824); Bory 

 iss. 6. 686. (1824' ; Marti, >s Ic. PI. Crypt. S3. (1834). 



Diagnosis.— fWcaJ Acrogem, with ringed spore-cases, growing on the back or edge of the 



leaves, distinct, and splitting irregularly. 



The vast number of plants of the Filical Alliance, collected under this head, are so 



much alike in many respects, that to separate them into distinct natural orders seems 



to me contrary to all the rules that govern Botanists in their limitation of such groups. 



The great mark by which they are known is the presence 

 on the spore-cases of a ring or band of coarse meshes, dis- 

 tinctly different from the tissue of their sides, and too strong 

 to be' broken through when the case opens to discharge its 

 contents. Whether the band is vertical or horizontal, 

 complete, incomplete, or otherwise, seems unconnected with 

 any physiological peculiarities that can be pointed out, and 

 to "be of no greater importance than for the subordinate 



The order consists for the most 

 re-cases on the back of 

 the exception of the 

 suborder called Hymen ophyllese, a group of thin, delicate, 

 membranous species, whose leaves open their edges for 

 the protrusion of a vein, over whose surface the spore-cases 

 are arranged. But, independently of all other reasons for 

 regarding the Hymenophyllese as a mere form of the great 

 order of Ferns, the existence of such genera as Cibotium, 

 Deparia, &c, among Ferns not Hymenophylleous, forbids 

 our attaching much importance to that peculiarity. A very 

 remarkable deviation from the common plan of structure 

 seems at first sight to occur in Osmundeae and Schizeae, in 

 which the spore-cases are collected together upon contracted 

 leaves, after the manner of the Adders' tongues ; but such 

 plants have no combining character, occurring among 

 Hymenophyllese as well. The passage of the true Ferns into neighbouring orders is 

 not v.-rv gradual. If we regard them as resting on the one hand upon Dansea-worts, 

 they can scarcely be said to touch Adders' tongues on the other, unless the great cha- 

 racter of the ringed spore-cases is left out of consideration, and then Osmundese may be 

 taken as the connecting link. 



The following proportions borne by Ferns to other plants in different latitudes will 

 serve to give some idea of the manner in which they are geographically distributed. 

 There is an enormous disproportion between Ferns and the rest of the Flora in certain 

 tropical islands, such as Jamaica, where they are 1-9 th of the Phsenogamous plants ; 

 New Guinea, where D'Urville found them as 28 to 122 ; New Ireland, where they were 

 as 13 to CO; and in the Sandwich Islands, where they were as 40 to 160; and it is 

 clear, from the collections of Wallich, that Ferns must form a most important feature 

 in the Indian Archipelago. Upon continents, however, they are far less numerous: 

 thus, in equinoctial America Humboldt does not estimate them higher than l-36th ; and 

 in New Holland Brown finds them l-:;7th. They decrease in proportion towardseither 

 pole; so that in France they are only l-63d ; in Portugal, 1-1 16th ; in the Greek 

 Archipelago, l-_.7th ; and in Egypt, l-971st. Northwards of these countries their pro- 

 portion again augments, bo that they form l-31st of the Phnsnogamous vegetation of 

 Scotland; l-3*>th in Sweden; 1-1 8th in Iceland; l-10th in Greenland; and 1 -7th at 

 North Cape. (See a very good paper upon this subject by D'Urville, in the Ann. des 

 & V<i7. 6.51. ; also Broicn's i.c to the Congo Voyage, 461.) Brown has observed 



(Flinden, o84), that it is remarkable, that although arborescent Ferns are found at the 

 southern extremity of Van Dieman's Island, and even at Dusky Bay in New Zealand, 



Fig. T.V.— l. Part of the leaf of Aspidium Lonchitis; 2. a magnified view of a morsel of Asp. 

 exaltatum. 



Kg. I.V. 



