THE SPRUCE FIR 277 



at the beginning of this process. The large vegetative 

 cell sends out a tube, which penetrates the tissue of 

 the nucellus. The vegetative nucleus passes into the 

 tube, but becomes disorganised, and has no further part 

 to play. So far the group of small cells within the 

 grain has remained unchanged. Now, however, the 

 end cell of the group, which is the generative cell, 

 divides into two. The stalk-cell behind them breaks 

 down ; the two generative daughter-cells are set free 

 and pass into the pollen tube (see Fig. 1 1 1 , C, 5). Their 

 nuclei have now become very large and granular. 



Pollination takes place in May, fertilisation not 

 until near the end of June. The interval in the Spruce 

 Fir is about six weeks ; in some other Conifers, such 

 as the Scotch Fir, Pinus sylvestris, and the Juniper, the 

 interval is very much longer. The pollen falls on to 

 the ovule in May of one year, but fertilisation is not 

 effected until June of the next year. 



To return to Picca : the pollen-tubes eventually grow 

 down through the nucellus as far as the embryo-sac. 

 They contain numerous starch -grains, which serve as 

 food during their growth. 



In the meantime the ovule has ripened. By the 

 time that the pollen-tubes have reached the embryo- 

 sac, it is completely filled with prothallus, and the 

 archegonia have been formed (see Fig. 112). After 

 the 20th of June the actual fertilisation takes place. 

 A pollen-tube penetrates the wall of the embryo-sac 

 just above the neck of an archegonium. It continues 

 to grow on, passes between the cells of the neck, 

 absorbs the ventral canal cell below, and reaches the 



