THE PLANT-CELL 



65 



cell, is much smaller and often actively motile, when it is termed a 

 Spermatozoid. The fusion of the latter with the egg constitutes fer- 

 tilization, or fecundation, without which the egg, except in rare cases, 

 is incapable of further development. The greater part of the sper- 

 matozoid is composed of nuclear matter, which fuses more or less 

 completely with the 

 nucleus of the egg- 

 cell before the latter 

 divides. 



The differentiation 

 of sexual cells has 

 taken place quite in- 

 dependently in sev- 

 eral widely separated 

 groups of plants, 

 where nearly every 



FIG. 47. A, single gamete. B, conjugating piano- 

 gametes of Ectocarpus siliculosus (x 790). C, male 

 gamete. D, female gamete of Cutleria multiftda 

 (X 960). E, egg. F, spermatozoid of Fucus vesi- 

 culosus (X300). (A, B, after BERTHOLD; C, D, 

 after REINKB.) 



gradation between 

 perfectly similar gam- 

 etes and well-marked 

 male and female cells 



may still be seen. 

 Thus in the Brown Algae many forms, including the largest ones, 

 produce no sexual cells at all, but only zoospores, which germinate 

 directly. Ectocarpus and various other allied genera produce simi- 

 lar motile gametes (Planogametes) ; Cutleria produces two kinds of 

 motile gametes, of very unequal size ; while in Fucus, the common 

 Rockweed, the non-motile egg-cells are enormously larger than the 

 active, ciliated spermatozoids (Fig. 47). 



BIBLIOGRAPHY 



'87. 1. De Bary, A. Comparative Anatomy of the Ferns and Flowering 



Plants. Oxford, 1887. 



'01. 2. Chamberlain, C. J. Methods in Plant Histology. Chicago, 1901. 

 '99. 3. Fischer, A. Fixirung, Farbung and Bau des Protoplasmas. Jena, 1899. 

 '96. 4. Haberlandt, G. Physiologische Pflanzenanatomie. Leipzig, 1896. 

 '98. 5. Henneguy, L. F. Lemons sur la Cellule. Paris, 1898. 

 '98. 6. Hertwig, O. Die Zelle und die Gewebe. Jena, 1898. 

 '82. 7. Sachs, J. Text-book of Botany. Oxford, 1882. 

 '00. 8. Strasburger, E. Histologische Beitrage, I-VI. Jena, 1890-1900. 

 '97. 9. - Das botanische Practicum. 3d edition. Jena, 1897. 

 '89. 10. Tschirch, A. Angewandte Pflanzenanatomie. Leipzig, 1889. 

 '98. 11. Van Tieghem, Ph. Traite" de Botanique. Paris, 1898. 

 '96. 12. Vines, S. H. Students' Text-book of Botany. London and New York, 



1896. 



'98. 13. Wiesner, J. Anatomie und Physiologic den Pflanzen. Vienna, 1898. 

 '00. 14. Wilson, E. B. The Cell in Development and Inheritance. New York. 



1900. (This contains an excellent bibliography of the subject.) 

 '93. 15. Zimmermann, A. Botanical Microtechnique. New York, 1893. 



