CONTRIBUTIONS TO BOTANY. 
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Excepting their amentiform diclinous inflorescence, there is 
nothing in the structure of the Betulacece, Cupuliferce, Arto- 
carpecE, and other consociate families, that offers any relation 
with the Gnetacece. 
In its aphyllous habit, its geniculated nodes, and vaginant 
bracts in lieu of leaves. Ephedra presents some similitude to 
Calligonum, Pterucoccus, and Calliphysa, with which it accords 
also in its tubular petaloid perigonium, seated in the axils of a 
general involucre — thus approaching the structure of the Erio- 
gonece, and more particularly that of Chorizantkus vaginatus, 
which has its stems furnished with opposite bracteiform leaflets 
united into a membranaceous sheath, as in Ephedra. The Poly- 
gonacece generally, indeed, agree with the Gnetacece in their often 
polygamo-moncecious or dioecious flowers, in their calycinoid in- 
volucres ; their petaloid perigonium ; their stamens often mona- 
delphous at the base; their usually one-celled ovary, with a 
single erect ovule, which (as I have shown) becomes fertilized, in 
the same manner as in the Gnetacece, by the direct influence of 
the pollen through an aperture in the apex of the cell, without 
the intervention of a placenta ; and, finally, in their indehiscent 
one-celled fruit, bearing a single erect albuminous seed, covered 
by two regular integuments, and enclosing an embryo with a 
superior radicle. However remarkable these analogies may be, 
which are in many respects shared with the Nyctaginacece, it is 
impossible to place the Gnetacece in a position near these families 
and their allies ; for the Oleracece of Endlicher form a most di- 
stinct and natural group, well characterized by the peculiar fea- 
ture of a curved embryo placed outside of a farinaceous albumen. 
Although the relationship of the Gnetacece with the Urticacece 
may not at first sight be apparent, still in many very essential 
points an analogy exists, which is well deserving of attention. 
The flowers in Urticacece are often diclinous, and in bracteated 
spikelets. It has been shown {ante, p. 146) that their soli- 
tary carpel, sometimes wanting a style, with sessile stigmata, 
has a pervious opening in the apex of its cell, through which the 
solitary erect ovule is directly fecundated by the pollen, without 
the intervention of any placenta. This erect ovule is always 
atropous, with two distinct integuments ; and its embryo, with a 
small superior radicle, is enclosed in fleshy albumen. In these 
remarkable particulars I know of no other order that so nearly 
approaches the Gnetacece. On the other hand, the Urticacece are 
very different in habit — in their usually (but not always) alter- 
nate leaves, in the form of their inflorescence, and in the struc- 
ture of the male flowers ; in the latter respect, however, a degree of 
analogy remains, for it generally happens in these, as in Ephedra, 
that the lobes of the perigonium are opposite to those of the 
