THE GYMNOSPERMAE : CONIFERALES AND TAXALES 687 



maturity there is little of it left except the cone of tissue at the micropylar 

 end, the cells of which are rich in starch. The tip of this cone becomes 

 partially disorganized at the time of pollination. 



The archegonia are essentially similar in structure to those of the Vascular 

 Cryptogams, differing only in the larger venter and smaller and simpler neck, 

 which is probably due to their enclosed position. The oosphere nucleus is 

 central and very large. In the cytoplasm there are a number of peculiar 

 vacuoles which appear to contain protein reserves and which stain like nuclei. 

 Thev are sometimes called the paranuclei (Fig. 688). 



Archegonium 

 neck cells 



Nucellui 







Oosphere nucleus 

 Jacket cells 





i ■• • 



♦ « 



Fig. 688.^P/?j!« sylvestris. Longitudinal section 

 through the apex of a female prothallus show- 

 ing an archegonium with oosphere nucleus 

 and paranuclei in the cytoplasm. 



Fertilization 



During April of the second year the pollen tube becomes active again, 

 and the male cells are formed from the antheridial body cell. The nuclei 

 of the tube cell, and the stalk cell, with the male cells, all pass down to the 

 apex of the pollen tube so that four nuclei are to be seen there. 



The pollen tube makes its w^ay down until it reaches the neck of one of 

 the archegonia, often throwing out short branches. The end of the tube 

 penetrates the neck, and the two nuclei wdth the complete male cells enter 

 the oosphere, where all but one male cell disintegrate. The nucleus of this 

 cell sHps out of its cytoplasm and unites with the oosphere nucleus. The 

 chromatin of the combined nucleus passes at once into mitosis and the two 

 sets of chromosomes mingle on the equatorial plate. The process is usually 

 completed in the last week of June. 



