conifer:^. ^ 525 



conveyed, probably in a soluble form, into the oosphere. In the Cupressineae, the 

 pollen-tube contains no starch-grains, but they appear abundantly in the nucleus of 

 the oospore. The pollen-tube remains completely closed during the whole process. 

 The first manifest result of fertilisation in the oospore is the division of its nucleus\ 

 In Pinus and Picea the nucleus usually travels to the lower end of the oospore ; it 

 then divides into two, and each of these divides again into two, and thus four nuclei 

 are formed which lie in one horizontal plane. Around each of them protoplasm 

 becomes aggregated, and thus a formation of cells takes place. It is from these cells 

 that the embryo or embryos are developed. Exactly the same takes place mjuniperus. 

 In Ginkgo {Sah'sburm) the nucleus divides, and this is repeated until a large number 

 of nuclei have been formed; a process of free cell- formation is then initiated round 

 these nuclei ; the cells become separated by cellulose walls, multiply by division, and 

 together constitute the embryo.] 



The mode of origin of the embryo is very different in the various families, but in 

 nearly all of them certain cells form a suspensor, and, by their great elongation, carry 

 the rudimentary embryo, which lies at the apex of the suspensor, through the base of 

 the archegonium out into the tissue of the endosperm where the embryo developes 

 into a young plant ^. In the Cupressineae the cell from which the embryo is de- 

 veloped (Fig. 355) becomes divided so as to give rise to three superposed cells, of 

 which, in Thuja occidentalism only the upper two become divided into four by longi- 

 tudinal walls, whilst in the lowest the rudiment of the embryo is formed by means of 

 oblique septa : the embryo is then extruded from the archegonium by the elongation 

 of the upper cells. In this case an oospore gives rise to a single embryo, growing 

 at first by means of an apical cell from which two rows of segments are cut off but 

 which it afterwards loses. In Juniperus, on the other hand, the lowermost of these 

 three cells becomes divided into four by intersecting longitudinal walls, which are 

 forced out by the elongation of the cells above them : these four cells become 

 rounded off and they separate, each giving rise to a rudimentary embryo. In this 

 case one oospore gives rise to four embryos, only one of which developes into a 

 plant. The first development of the suspensor in the Abietinese is somewhat 

 different. The four cells lying side by side in one plane become divided by trans- 

 verse septa so as to form three tiers ; the cells of the second tier grow out into long 

 coiled filaments, whereas those of the uppermost tier remain in the oospore as a 

 rosette : the four cells of the lowest tier, which have been forced into the endosperm 

 by the elongation of those above them, are repeatedly divided and thus contribute to 

 the elongation of the suspensor ; the four rows of cells then separate, each bearing 

 a terminal cell from which the rudiment of the embryo is developed in such a 

 manner that the possibility of the existence of an active apical cell is excluded^. 

 Thus in the Abietineae also four rudimentary embryos are developed from a single 



^ [Strasburger, Zellbildung und Zelltheilung, 3rd edition, p. 46.] 



"^ [Strasburger has observed (Angiospermen u, Gymnospermen, p. 149) that in Cephalotaxus For- 

 tunei and in Araucaria hradliana certain cells at the apex of the embryo are thrown off when it has 

 made its way into the endosperm.] 



^ [Skrobiszewski has pointed out (Bull, de la Soc. Imp. des Natural, de Moscow, 1873), and his 

 observations have been confirmed by Strasburger (Die Angiospermen und die Gymnospermen), that 

 the embryo of Pinus Slrobus, unlike that of the other Abietinese, grows in length by means of a two- 

 sided apical cell.] 



