CONTRIBUTIONS TO BOTANY. 
153 
ways polyembryonoiis), previous to the development of the several 
embryo-sacs and their suspending threads, the former are con- 
stantly first discernible in distinct areolar cells in the nucleus, 
arranged, as in Cycas, in a circular series in the summit of the 
amniotic body : these sacs descend, each separately suspended 
by its own elongated thread; but generally only one of them 
becomes fertilized. The further progress of this growth, and the 
increment of the embryo, which becomes surrounded by an 
albuminous mass that pushes upward the amniotic body, and 
remains persistent on it like a calyptriform cap, is quite analo- 
gous to the growth described by Miquel in Cycadacea, and very 
different from that of Gnetum. It is remarked by Brown that 
each suspending thread appears formed of about four simple 
tubes connected together but slightly, for he found them easily 
separable from one another without laceration of their surfaces ; 
and this fact gives additional force to the conclusion before 
mentioned regarding the nature and origin of the suspensor. 
Still further evidence is given by Schleiden, who traced the en- 
trance of pollen-tubes into the areolar cavities before described, 
and into the embryo-sacs, with which they remained permanently 
connected. The growth and development of these several em- 
bryo-sacs in each ovule, and their attachment to suspending 
threads in Pinus, Thuja, and Taxus, are minutely described and 
figured in the interesting researches of Mirbel and Spach*, 
published about the same time, and confirming all the observa- 
tions of Brown : they describe also each suspending thread as 
being formed of five or six boyaux or simple tubes agglutinated 
together, each being hollow and filled with granular fluid or 
such fovillffi as are usually found in the boyaux of pollen. 
It has been the opinion of many botanists that the existence 
of annularly dotted vessels in the wood of the Gneiacea affords 
evidence of their close affinity with the Conifera ; but even if this 
had been true, it would have claimed, on its own merit, a very 
secondary importance, since we find such vessels also in the 
Winteracece, Canellacece, Schizandracece, &c. Dr. Bindley says of 
Gnetum that its wood “ is composed of woody fibres and of annular 
and reticulated vessels lying scattered sparingly among tubes of 
woody fibre’H" He says also that its wood is zoneless. These 
circumstances led that eminent botanist to conclude that the 
Gnetacece are very distinct from the Conifera, forming a link 
between Taxinea and Piperacece : this, at least, was his opinion 
in 1834, although other considerations induced him afterwards 
to modify his view of the place of this small family in the sys- 
* Ann. Sc. Nat. 2 ser. xix. pi. 8, 9, 10, 11. 
t Bot. Reg. vol. XX. pi. 1686. 
VOL. II. X 
