CYTOLOGY OF REPRODUCTION IN PLANTS 



149 



tube to come into contact with the gametophyte near the arch(!gonia. 

 There the tube Hberates the sperms which make their way between the 

 archegonial neck cells into the egg. 



Fig. 107. — Portion of ovuh ot i(\i id (l)ioon) 

 at the time of fertilization Pollen tubes gi owing 

 in the nucellar tissue are developing sperms and 

 discharging them into the pollen chamber above 

 the female gametophyte. The large archegonium 

 at the right is about to be entered by a sperm. In 

 the one to the left the sperm has entered, leaving its 

 cytoplasmic sheath in the upper end of the egg 

 while its nucleus has fused with the egg nucleus. 

 {Reconstructed from several sections by C. J. 

 Chamberlain.) 



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lUS. — Syngamy and early 

 embryogeny in a cycad (Stangeria). 

 a, sperm nucleus uniting with nucleus 

 of large egg; blepharoplast and cilia 

 in upper end of egg. 6, nuclear 

 division without cytokinesis in prog- 

 ress in young zygote, c, cocnocytic 

 embryo becoming cellular. {After 

 C. J. Chamberlain.) 



The male gamete in conifers may enter the egg as a complete cell or 

 only a nucleus. In cycads the whole sperm enters with its large nucleus, 

 cytoplasmic layer, spirally coiled blepharoplast, and many cilia. The 

 nucleus soon becomes free from the cytoplasm and motor apparatus 

 and advances alone to the egg nucleus, the two then fusing (Fig. 108, a). 



