280 



STRUCTURAL BOTANY 



The four free nuclei now become disorganised ; the 

 tier of four cells next below them undergoes little 

 change, and remains in its original position. The 

 third layer, however, s in Fig. 114, E and F t elongates 

 enormously, forming the suspensor, 

 which here consists of four parallel 

 cells. The lowest group of four cells 

 is pushed forward by the suspensor 

 deep into the middle of the pro- 

 thallus. It is this lowest group, 

 c in Fig. 114, E and F, which 

 alone forms the actual embryo. 



In the Spruce Fir only one 

 embryo can be formed from each 

 archegonium. All the archegonia, 

 however, may be fertilised; so, for 

 a time, from three to five develop- 

 ing embryos may be present side 

 by side in the prothallus of the 

 same ovule. One, however, always 

 gains the upper hand, and in the 

 ripe seed only this one remains. 

 In some other Conifers, such as the 

 Scotch Fir, the four cells of the 

 suspensor separate from each other, 

 and each bears a separate embryo 

 at its end. In this case, therefore, 

 each archegonium gives rise to four embryos, and 

 altogether there may be from twelve to twenty in 

 the young seed. Here also, however, only one out of 

 the whole number comes to perfection. 



FIG. 115. Longitud- 

 inal section of the 

 embryo of Picea 

 taken from a ripe 

 seed, cp, root-cap ; 

 pi, growing point 

 of root ; m, pith ; 

 cy, vascular tissue 

 of cylinder ; h, hy- 



Socotyl ; c, cotyle- 

 ons, of which only 

 two are shown. 

 Magnified 10 dia- 

 meters. (After 

 Strasburger.) 



