GROUP IV. GYMNOSPERMJE. 



425 



planes at right angles to each other, so that the lower end of the 

 oospore is occupied by a group of four cells lying in one plane ; 

 these cells then divide by transverse walls, "so that three tiers of 

 four cells each are formed ; of these, each cell of the middle tier 

 grows out into a long unicellular suspensor ; those of the upper tier 



FIG. 249. Fertilisation, and early stages in the embryogeny, of Picta excelsa (x90; 

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

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

 on female pronucleus. C Fusion of male and female pronnclei. 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 snspensors, bearing 

 the single embryo at their lower end. 



simply maintain the connexion of the suspensors with the rest of 

 the oospore; those of the lowest tier, whilst also contributing to the 

 suspensors, -each give rise to an embryo : from the cells at the base 



