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I902I 



A MORPHOLOGICAL STUDY OF THUJA 



255 



nium may be fertilized. In fig. ly the proembryo is well 

 advanced, while the ventral nucleus has formed a group of four 

 cells — three of which are shown in the figure, as it was drawn 

 from a single section — which certainly suggests a proembryo in 

 the four-celled stage. Another preparation shows eight cells 

 with indications that walls are soon to appear. The proba- 

 bility of such a fertilization is strengthened by finding occasion- 

 ally in the same ovule embryos growing upward into the nucel- 

 lus {^fig. -?/), as well as downward into the endosperm. These 

 embryos are so old that it was not possible to determine defi- 

 nitely if their suspensors are connected with a common arche- 

 gonium, but such appears to be the case. The embryos grow- 

 ing upward into the nucellus are not so vigorous as those grow- 

 ing downward into the endosperm. 



The 



FERTILIZATION. 



contents of the pollen tube are discharged into the 

 space immediately above the archegonium complex, but it does 

 not appear that very much enters the ^'g'g. Traces of the cyto- 

 plasmic contents of the pollen tube can usually be seen in the 

 upper end of the egg, usually showing as densely staining 

 masses. In some cases the tube and stalk nuclei enter the ^%%, 

 in others only one of these nuclei enters, but in the great major- 

 ity of cases they do not enter the cytoplasm of the o,^^ at all, 

 but disorganize in the space above the archegonia. Fig. 14 shows 

 the male cell entering the (^gg. At this stage, in general, the 

 large vacuole which occupied the center of the ^g% has disap- 

 peared, and the ^gg nucleus has taken its place. Soon after 

 coming in contact with the ^gg the male nucleus slips from its 



sheath and moves downward toward the e 



nucleus. The 



actual breaking out of the male nucleus from its cytoplasmic 

 sheath was not observed, but numerous preparations showed 

 remnants of the sheath in the upper end of the t.g%. Fig. 15 

 shows the male cell just after its escape from the sheath, and 

 also shows one of the rare cases in which the large vacuole is 

 still present at this stage. The male nucleus passes down, and 



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