398 
system is developed, of their pinnate leaves with a gyrate vernation, and their 
naked o\niles borne upon the margin of contracted leaves, as the thecae of 
Ferns are upon the fronds of Osmunda. Their affinity with Equisetum, to 
which they were formerly joined, consists more in their want of flowers, and 
in the presence of anmflar ducts, than in any similarity of habit. Lycopo- 
diaceae are readily known by their axillary thecae, dehiscing by two regular 
valves. Marsileaceae are so very diflerent, that it is difficult to find points of 
comparison between them. 
The organ in Ferns which deserv’es 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 imphes 
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 Acrogens. 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 midrib, and the theca itself the lamina, 
the edges of which are united.” I was led to this opinion, first, by the per- 
suasion that there w’^as 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 obser- 
vation has shewn us that the leaves of Flowering plants 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 Barley 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 thecae, or from the margin ; and I was particularly struck with a vivi- 
parous Fern, of which a morsel was given me by Dr. WaUich, where the 
young plants form little clusters of leaves in the place of sori. Upon exa- 
mining these young plants, I saw that the more perfect, though minute, 
fronds were preceded by still more minute primordial leaves or scales, the cel- 
lular 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 consi- 
deration of the botanical wmdd. It is, however, necessary that I 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 striated thecse, or with wffiat is called a broad tranverse 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 smTounds it and also from its internal substance, w'hich 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 areolae of cellular tissue at the 
base and apex, connected by extended cellules of the same description, as in 
