313 . 



mencemcnt of their growth is extremely different from the cotyledon of 

 Monocotyledons, which pre-exists in the seed and never quits it, but swells 

 during germination, and acts as a reservoir of nutriment for the young plant- 

 let. He most properly regards it as -an imperfectly developed primordial leaf. 

 The organ in Ferns which deserves the most particular attention is the 

 theca, or case that contairls the reproductive matter. By many it is named 

 capsule ; but as that kind of pericarpium 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, nothing of which kind is found in the theca of Ferns, it 

 is not necessary to insist upon the impropriety of applying such a name 

 to any sporule-case in Cellulares. Easy as it is to shew that the theca 

 is not analogous to a capsule, it is far less so to demonstrate with what 

 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, in the Outlines of the First Principles of Botany, I 

 ventured to hazard the following theory (par. 533): "The thecse may be 

 considered minute leaves, having the same gyrate mode of developement as 

 the ordinary leaves of the tribe ; their stalk the petiole, the annulus the mid- 

 rib, 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 

 modifications of leaves ; and, secondly, by the examination of viviparous 

 species. . I need not here remark, that observation has shewn us that the 

 leaves of Vasculares have the power of producing leaf-buds from their margin 

 or any point of their surface ; and the instance I have adduced in Grasses of 

 a monstrous Wheat shews that they can produce flower-buds also. I found 

 in Ferns, which are exceedingly subject to become viviparous, that the young 

 plants often grow from the same places as the thecse, or from the margin ; 

 and I was particularly struck with a viviparous Fern, of which a morsel was 

 given me by Dr. Wallich, where the young plants form little clusters of leaves 

 in the place of sori. Upon examining these young plants, I saw that the 

 more perfect, though minute, fronds were preceded by still more minute 

 primordial leaves or scales, the cellular tissue of which had nearly the same 

 arrangement as the cellules of the theca ; and I was most especially struck 

 with the resemblance between the midrib of one of these scales and the 

 annulus of a Polypodium. A view of the thecse of various annulate Ferns 

 produced a conviction of the truth of the theory I had formed, which I 

 now submit with much deference to the . consideration of the botanical 

 world. It is, however, necessary that 1 should here add what is only 

 implied in the little work from which the foregoing extract is taken, that this 

 explanation applies only to the gyrate Ferns. With regard to those with stri- 

 ated thecae, or with 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 

 theca is formed, So much developed ; or the theca may be with stilL more 

 probability 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 internal tissue of an anther sepa- 

 • rates from the valves under the form of pollen. This conjecture is, I think, 

 very much confirmed by the anatomical structure of those striated thecae 

 which consist of a cluster of sporule-like 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 thecae as those of Par- 

 keria. In Ophioglossese another kind of provision is made for the produc- 

 tion of sporules, which in those plants seem to have no theca whatever 



