ACROGENS.] 



FILICALES. 



75 



and their naked ovules borne upon the margm of contracted leaves, as the spore-cases of 

 Ferns are upon the leaves of Osmunda. To Coniferous Gynniospemis they also advance 

 very closely through Sahsburia, whose leaves might be mistaken for those of a Fern. 

 The afiinity of Ferns with Equisetum, consists more in a want of flowers, and the 

 presence of annular vessels, than in any similarity of habit. Clubmosses are readily 

 known by their axillary spore-cases dehiscing by regular valves. Pepperworts are so 

 very dilTerent, that it is difficult to find points of comparison between them, except the 

 gyrate leaves of some of the genera. 



The organ in Ferns which deserves the most particular attention is the theca, or 

 case that contains the reproductive matter. By many it is named capsule ; but as that 

 kind of pericarp is essentially connected with the power of conveying fertilisation from 

 the male apparatus to the ovules, and implies the existence of a certain definite relation 

 between the various parts that it contains, nothmg of which kind is found in the spore- 

 case of Ferns, it is not necessary to insist upon the impi'opriety of applj-ing such a name. 

 Easy as it is to show that the spore-case is not analogous to a capsule, it is far less so to 

 demonstrate with Avhat organs or modifications of organs it really has an analogy. I am 

 not, indeed, aware that this had been attempted, all botanists seeming to consider it a 

 special organ, until, m the Outlines of the First Principles of Botany, I ventured to 

 hazard the followuig theory : " The thecse may be considered minute leaves, haATug the 

 same g>Tate mode of development as the ordinary leaves of the tribe ; their stalk the 

 petiole, the annulus the midrib, and the theca itself the lamina, the edges of which are 

 united." I was led to this opinion, first, by the persuasion that there was no special 

 organ in Ferns to perform a function which in flowering plants is executed by modifica- 

 tions of leaves ; and, secondly, by the examination of A-iviparous species. Observation 

 has shown us that tlie leaves of flowering plants have the power of producing leaf-buds 

 from their margm or any point of theii' sm-face ; and in certain kinds of Grasses it has 

 been found that they can produce flower-buds also. In Ferns, which are exceedingly 

 subject to become viviparous, the young plants often gi'ow from the same places as the 

 spore-cases, or from the margui ; and m a Adviparous Fern, of which a morsel was given 

 me by Dr. WalHch, the young plants form little clusters of leaves in the place of sori. 

 Upon examining these young plants, it appears that the more perfect, though minute, 

 leaves are preceded by stiD more minute primordial leaves or scales, the cellular tissue 

 of which has nearly the same arrangement as the cellules of the spore-case ; and the 

 resemblance between the midi'ib of one of these scales and the ring of a Pol}-podium is 

 striking. It is, however, necessary to add, what is only impUed in the little work from 

 which the foregoing extract is taken, that this explanation applies only to the gp'ate 

 Ferns. With regai'd to those with striated spore-cases, or y\\t\\ what is called a broad 

 transverse ring, they may either be considered not to have the midrib of the young 

 scale, out of which the case is supposed to be formed, so much developed ; or the case 

 may be still considered a nucleus of cellular tissue, separating both from that which 

 surrounds it and also from its internal substance, which latter assumes the form of 

 sporules, in the same way as the intenial tissue of an anther separates from the valves 

 under the form of pollen. This conjectm-e seems confirmed by the anatomical struc- 

 ture of those stinated cases which consist of a cluster of spore-hke areolae of cellular 

 tissue at the base and apex, connected by extended 

 cellules of the same description, as in Gleichenia ; 

 and is far from being weakened by such cases as 

 those of Parkeria. In Ophioglossura another kind 

 of provision is made for the production of spores, 

 which in that genus seem to have no spore-case 

 beyond the involute contracted segments of the 

 leaf which bears them. What are called the 

 thecse in Ophioglossum seem more analogous to 

 the involucre of Marsilea. 



It has been thought that sexes occur in 

 these plants, and different parts have been 

 pointed out as the anthers ; more especially 

 little threads which contain a grumous matter, 

 sometimes exuded in the form of a crust, and 

 spring up among the spore-cases. Some pro- 

 bability seems to have been given to the presence of anthers by what has been con- 

 sidered an occurrence of Mule ferns, principally belonging to the genus Gymnogramma, 

 some account of which will be found in the Gardeners' Chronicle 1844, p. 500 ; but it 

 does not appear to me that there is good evidence to show that such instances are 



Fig. LIII.— Young spore-cases and antheridia of Polypodium effusum. Link. 



Fig. LIII. 



