310 



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

 and acts as a reservoir of nutriment for the young plantlet. 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 contains the reproductive matter. By many it is named capsule ; 

 but as that kind of pericarpium is essentially connected with the power of 

 conveying fertilization from the staminiferous organs to the ovules, and im- 

 plies 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 neces- 

 sary to insist upon the impropriety of applying such a name to any sporule-case 

 in Cellulares. Easy as it is to show that the theca is not analogous to a cap- 

 sule, 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 attempt- 

 ed, 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 thecal 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 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 exe- 

 cuted by modifications of leaves ; and, secondly, by the examination of vivipa- 

 rous species. I need not here remark, that observation had shown 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 shows 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 per- 

 fect, 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 thecal 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 I 

 should here add what is only implied in the little work from which the fore- 

 going extract, is taken, that this explanation applies only to the gyrate Ferns. 

 With regard to those with striated theca-, or with what is called a broad trans- 

 verse 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, sepa- 

 rating 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 separates 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 areoloe 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 

 Parkeria. In Ophioglosseae another kind of provision is made for the produc- 

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

 the involute contracted segments of the frond which bears them. What are 

 called the thecse in Ophioglosseae are improperly so termed, and are much more 

 analogous to the involucrum of Marsilea. 



