SPERMATOPHYTES 



217 



there is much nucellar tissue to be traversed before the female gameto- 

 phyte with its archegonia is reached. For the first time, the pollen 

 tube acts as a carrier of the male cells, the 

 body cell, which is to divide, entering the 

 tube and remaining near its tip as it ad- 

 vances through the tip of the nucellus (fig. 

 479). The tube may advance directly 

 towards the archegonia or it may pursue a 

 devious route, in some cases not reaching 

 the archegonia until during the second 

 season. When an archegonium is reached, 

 its neck is broken through and the contents FlG - 48 - ~ Male gametophyte 



....... .. , j. , .of Dacrydium (one of the podo- 



of the tip of the pollen tube are discharged carps) at shedding stage of pollen> 



into the egg (fig. 481). showing four vegetative cells, stalk 



Embryo. In the development of the and bod y cells ( formed b ? the 



....... . generative cell), and the tube 



embryo from the fertilized egg, there is a nucleus. After Miss YOUNG. 



variable amount of free nuclear division, 



from four free nuclei (Torreya, fig. 482) up to thirty-two^ in strong 



contrast with the very numerous free nuclei appearing in the embry- 



ogeny of cycads and of 

 Ginkgo. After the free 

 nuclei are formed, walls 

 appear, and the resulting 

 tissue (proembryo) fills the 

 egg. In general, there are 

 about three tiers of cells in 

 the proembryo, the lowest 

 (innermost) one usually con- 

 sisting of a single cell, so 

 that the proembryo has a 

 general conical outline (fig. 

 483). An elongation of cells 

 begins in the upper (outer- 

 most) tier (fig. 484), and 

 this is continued by the 

 middle tier> so that the 



FIG. 481. Fertilization of Torreya: the pollen terminal cell, which is to 



tube has discharged its contents into the egg, and . . . 



the male and female nuclei are f using. - After form the embryo, IS thrust 



COULTER and LAND. out of the archegonium and 



