CONTRIBUTIONS TO BOTANY. 
155 
Urticacece, which, being always united in bundles, give rise to 
its finely striated surface ; it is covered by a thick, tough epi- 
dermis, of the texture of parchment, and which follows the si- 
nuosities of the striatures. Upon the ridges of the striae a 
number of prominent horny excrescences occur, which occasion 
its scabridity; and in the hollows between the ridges are seen a 
number of black longitudinal specks, which appear almost like 
stomata that have become closed by a deposit. 
Thus far it has been endeavoured to show that the order 
GnetacecB is not allied to any of the Gymnospermous families, 
with which it has been associated by most botanists. It will 
now be necessary to pass in review the points of analogy that 
exist between it and other exogenous orders, in order to judge 
of its true affinities. 
Blume, when he founded the order, as before stated, suggested 
the relationship of the Gnetacece with Casuarina, to which genus 
it certainly offers many points of approximation. Casuarina 
resembles Ephedra in the following’particulars : — in the vaginant 
sheaths that encircle the nodes of its branchlets, where they 
occupy the place of leaves ; in its spicated inflorescence, with 
diclinous flowers ; in the persistence of the involucral leaflets, 
which afterwards enclose the fruits ; in its bifid perigonium, even 
more deciduous than that of Ephedra, for it is cari’ied away by 
the stamen as it grows upward in the act of aestivation ; in its soli- 
tary stamen, very analogous to that of Gnetum ; in its one-celled 
ovary, with an ascending ovule ; and in its indehiscent one-celled 
fruit, with a single erect seed, containing an embryo imbedded 
in albumen, with a superior radicle. Casuarina, however, differs 
from both Gnetum and Ephedra in its straight, lofty, solid, woody 
trunk ; in its ovary with two lengthened styles (being probably 
formed normally of two combined carpels, one of which is always 
abortive, and which contains two ovules) ; in its fruit, with a 
samariform epicarp, a mesocarp replete with very numerous deli- 
cate spiral vessels, and a solid testaceous endocarp ; and, finally, 
in the development of its seed, the anomalous circumstances 
attendant on which have been only imperfectly understood*. 
* I have examined the seeds of Casuarina equisetifolia many times, 
always with the same result ; and as my analysis shows a strueture very 
different from what is recorded of it, I will state the details. The descrip- 
tion given by Endlieher of this structure (Gen. Plant, p. 271) is altogether 
incorrect. It is well known that the fruits are contained in globular or 
oblong strobiliform heads, each separate fruit being enelosed in a cell 
formed of two coriaceous valves, which are the persistent involucels of the 
spieated flowers, which valves stand right and left in regard to the axis. 
Each fruit is fixed to the bottom of its enelosure by a small basal hilum ; 
it is somewhat samariform, oblong and eompressed ; the upper moiety 
(being a portion of the extended epicarp) forms a thin membranaceous 
X 2 
