53° 
PHANEROGAMS. 
epidermal cells, situated in the ' cupule' formed by the bracts, begin to divide, and 
then divisions take place in the hypodermal cells ; by this means a number of 
protuberances are formed, usually six or eight, in a whorl, which are the rudimentary 
ovules. Around each of these the external integument begins to grow up : when the 
external integument covers about two-thirds of the nucellus, the middle integument 
begins to be formed, and this is immediately followed by the appearance of the 
innermost integument. The nucellus elongates above the insertion of the external 
integument, and in consequence the cells of which it consists can be distinctly seen 
to be arranged in longitudinal rows. The terminal cell of one or more of these 
rows, which is therefore hypodermal, elongates, and thus the archesporium is consti- 
tuted. These cells now undergo divisions, cells being cut off from them towards 
the free surface of the nucellus ; these cells thus cut off form part of the tapetum, 
the larger cells beneath them being the mother-cells of the embryo- sacs. Of these, 
one only gives rise to an embryo-sac, the others becoming obliterated. The forma- 
tion of the endosperm begins with the division of the nucleus of the embryo-sac : 
a number of nuclei are formed by repeated division, and around these free cell- 
formation takes place. 
The development of the ovule of Ephedra is much the same as that above 
described in Gnetum. The endosperm of Ephedra produces from three to five 
archegonia, with an elongated oosphere, a distinct canal-cell, and a long neck con- 
sisting of rows of cells. After fertilisation the nucleus of the oospore divides, and 
the two new nuclei separate and travel towards the opposite ends of the cell. Here 
they undergo division, and this is repeated until usually eight nuclei have been 
formed. Around these a process of free cell-formation now takes place, and each of 
the cells thus formed becomes enclosed in a cellulose wall. Each of these cells, 
which are quite distinct from each other, now grows out into a tube which escapes 
from the archegonium and penetrates into the endosperm : a small portion of the 
tube is now cut off by a transverse septum near the apex. It is from this cell 
that the embryo is developed. It divides into two by a transverse wall parallel 
to the first, and these two cells grow and divide in various directions ; sometimes a 
two-sided apical cell is formed by means of which the embryo grows.] 
A small cell is formed in the pollen-grain of Ephedra as in that of the Cupres- 
sineae. 
The Histology of Gymnosperms. From the abundant though still unsifted material 
I will only adduce a few particulars as a contribution to the special characteristics 
of this section. 
The Fibro-'vascular Bundles ^ are similar in their structure to those of Dicotyledons.^ 
There is a system of bundles common to the stem and leaves; the portions which 
^ Mohl, Bau des Cycacleenstammes (Verm. Sehr. p. 195). — Kraus, Bau der Cycadeen-Fiedern 
(Jahrb. f. wiss. Bot. \o\. IV. p. 329). — Geyler, Ueber Gefässbundelverlauf bei Coniferen (ditto, 
vol. VI p. 68). — Thomas, Vergl. Anat. des Conifer-Blattes (ditto, vol. IV. p. 43). — Mohl, Ueber die 
grossen getüpfelten Röhren von Ephedra (Verm. Sehr. p. 269). — J. D. Hooker, On Welwitschia 
(Trans. Linn. Soc. vol. XXIV). — Dippel, Histologie der Coniferen (Bot. Zeitg. 1862 and 1863). — 
Rossmann, Bau des Holzes (Frankfurt-a-M. 1863). — Mohl, Bot. Zeitg. 1871, — [Bertrand, Anat. comp, 
des tiges et des feuilles chez les Gnetacees et les Coniferes, Ann. Sei. Nat., ser. 5. XX. — Bower, On 
Welwitschia, Quart. Journ, Micr, Sei. 1 881.— De Bary, Vergleichende Anatomie der Vegetationsorgane, 
1877-] 
