GYMNOSPER MA E. ONE TA CEA E. 



341 



two pairs of small decussate leaves ; the lower ones are entirely free, falcately curved 

 and acuminate, the upper ones broadly spathulate and cohering at the base into a 

 compressed tube. Inside this tube are six stamens, monadelphous below, with 

 cylindrical filaments and terminal spherical trilocular anthers opening by a three- 

 rayed fissure at the apex. The centre of the flower is occupied by a single erect 

 orthotropous sessile ovule with a broad base, and with no investment except a simple 

 integument which is prolonged into a style-like tube with its margin expanded into 

 a disk ; but the nucellus has no embryo-sac and is sterile. In the female flowers the 

 perianth is tubular and much compressed, slightly winged and quite entire ; there is 

 no indication of male sporophylls ; the ovule, which of course has an embryo-sac, is 

 completely enveloped in the perianth and is of the same shape as the ovule in the 

 male flower, with the difference only that the elongated apex of the integument is only 

 simply slit and not expanded into a disk. The 

 cones when ripe are nearly two inches long 

 and scarlet in colour ; the scales are persistent ; 

 the perianth increases considerably in size and 

 becomes broadly winged, and its cavity narrows 

 above into a slender canal, through which the apex 

 of the integument passes. The seed, which is of 

 the same shape as the ovule, contains a copious 

 endosperm, in the centre of which is the dicoty- 

 ledonous embryo; the embryo is thick at its 

 radicular end and attached by it to a very long 

 spirally-coiled suspensor. The embryo-sac (ma- 

 crospore) is formed in exactly the same way as 

 in the Coniferae, in Larix for example ; Gnetum 

 Gnemon has several ' embryo-sac-mother-cells.' 

 The mode of development of the embryo from 

 the oospore is peculiar 1 . In Ephedra (Fig. 263) 

 the nucleus of the oospore divides first into 

 two free daughter-cells ; by repeated bipartition 

 four and then eight nuclei are formed. Then 

 cells are formed round these free nuclei ; they 

 collect protoplasm, which is disposed round them 

 in radiating lines and then invests itself with 

 a cell-wall. Each of the free pro-embryonal 

 cells thus formed developes into a tube which pierces the side-wall of the arche- 

 gonium, and parts off at its apex a small cell containing much protoplasm from 

 which the embryo is formed ; but one only of these many rudimentary embryos 

 comes to complete development This mode of development of the embryo is 

 not so very different from that which has been already described in the case 

 of Pmus, for example, as may at first sight appear; the chief distinction is that 



^IG. 263. Commencement of formation of the 

 embryo in Ephedra altissima. I oosphere before 

 fertilisation with only one nucleus n. //After fertili- 

 sation ; the nucleus has divided. /// four nuclei in the 

 oosphere. /K formation of cells round the nuclei V 

 completion of formation of cells. VI development of 

 the pro-embryos, which have each divided off a 

 small cell at their apex. Kz canal-cell, n nucleus, p 

 pollen-tube, Km pro-embryo. After Strasburger, 

 magn. about 30 times. 



1 [According to Bower, The Germination and Embryology of Gnetum Gnemon (Q. J. M. S. 

 1882), the embryo in Gnetum Gnemon is not found at the extremity of the suspensor until after the 

 seed is separated from the parent plant, and its development corresponds closely with the type in 

 Gymnosperms. A ' feeder ' is formed on the hypocotyleddnary axis as in Welwitschia.'] 



