78 



POLYPODIACE^. 



[ACROGENS. 



Order XXIV. POLYPODIACEjE.— Ferns. 



GyratEB, Sioartz Synopsis Filicum, (1806).— Filices verae, Willd. Sp.Pl. 5. 99. (1810.)— Polypodiaceae, 

 R. Brown Prodr. 145. (1810) ; Agardk Aph. 116. (1822) ; Kaulfuss Enumeratio, 55. (1824) ; Borp 

 in Diet. Class. 6. 586. (1824) ; Martins Ic. PL Crypt. 83. (1834). 

 Diagnosis. — Filical Acrogens^ with ringed spore-cases, growing on the had or edge of the 

 leaves, distinct, and splitting irregularly. 

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

 much aUke 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 presen.ce 

 on the spore-cases of a I'ing or band of coarse meshes, dis- 

 tuictly 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 imconnected with 

 any physiological peculiarities that can be pointed out, and 

 to be of no greater importance than for the subordinate 

 purposes of classification. The order consists for the most 

 pai't of species bearing theu" spore-cases on the back of 

 leaves, usually named fronds ; with the exception of the 

 suborder called Hymenophylleae, a group of thin, dehcate, 

 membranous species, whose leaves open their edges for 

 the protinision of a vein, over whose sui'face the spore-cases 

 are arranged. But, mdependently of all other reasons for 

 regarding the H\'menophyllese as a mere form of the great 

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

 Deparia, &c., among Ferns not Hpnenophylleous, forbids 

 om- attaching much importance to that pecuharity. A very 

 remarkable de^^ation from the common plan of structm'e 

 seems at first sight to occur in Osmundese and Schizese, 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 

 The passage of the ti'ue Ferns into neighbomnng orders is 

 not very 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 Osmimdese may be 

 taken as the comiecthig link. 



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

 serve to give some idea of the manner in which they are geogi^aphically distributed. 

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

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

 New Gumea, where D'Ur>'ille found them as 28 to 122 ; New Ireland, where they were 

 as 13 to 60 ; and in the Sandwich Islands, where they were as 40 to 160 ; and it is 

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

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

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

 in New Holland Brown finds them l-37th. They decrease in proportion towards either 

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

 Archipelago, 1-22/^th ; and in Egypt, l-971st. Northwards of these countries their pro- 

 portion again augments, so that they form l-31st of the Phtenogamous vegetation of 

 Scotland; l-35th in Sweden; 1 -1 8th m Iceland ; 1-lOth in Greenland; and l-7th at 

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

 Sc. Nat. 6. 51. ; also Brotvn^s Appendix to the Congo Voyage, 461.) Brown has observed 

 {Flinders, 584), that it is remarkable, that although arboi'escent Ferns are found at the 

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



Fig. LV. — 1. Part cf the leaf of Aspidium Lonchitis ; 2. a magnified view of a morsel of Asp. 

 exaltatum. 



Fig. LV, 

 Hj-menophyllese as well. 



