530 PJIA NER OGA MS. 



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 wnth 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 Gnelum. 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- 

 sinese. 



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 Cycadeenstammes (Verm. Schr. p. 195).— Kraus, Bau der Cycadeen-Fiedern 

 (Jahrb. f. wiss. Bot. vol. IV. p. 329).— Geyler, Ueber Gefassbundelverlauf bei Coniferen (ditto, 

 vol. VI p. 68). — Thomas, Vergl. Anat. des Conifer-BIattes (ditto, vol. IV. p. 43). — Mohl, Ueber die 

 grossen getiipfelten Rohren von Ephedra (Verm. Schr, 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. Sci. Nat., ser. 5. XX. — Bower, On 

 Welwitschia, Quart. Journ. Micr. Sci, 1881.— De Bary, Vergleichende Anatomieder Vegetationsorgane, 

 1877.] 



