472 



PART III. THE CLASSIFICATION OF PLANTS. 



tier simply maintain the connexion of the suspensors with the 

 rest of the oospore ; those of the lowest tier, whilst also contribu- 

 ting to the suspensors, each give rise to an embryo, from the cells 



FIG. 298. Fertilisation, and early stages in the embryogeny, of Picea excelsa ( x 90 ; 

 after Strasburger). A Oosphere, with nucleus on, and canal-cell cl. B Fertilisation in pro- 

 gress : p pollen-tube; sn nucleus (male pronucleus) of the male cell now in the oosphere ; 

 on female pronucleus. C Fusion of male and female pronuclei. D Commencing cell-forma- 

 tion at the chalazal end of the oospore ; E a further stage : F three tiers of four cells each 

 have been formed : G the cells of the middle tier have elongated into suspensors, bearing 

 the single embryo at their lower end. 



at the base of which one or more embryonal tubes are developed 

 which grow backward along the suspensor. Picea excelsa departs 

 from this type in that the suspensors remain coherent, bearing at 



