226 Fertilization and Hybridization 



introduced. In certain filamentous algae (Spirogyra) Ge- 

 rassimow succeeded in producing cells without nuclei ; 

 they retained life for several weeks, feeding vigorously, 

 but nevertheless they always perished without any repro- 

 duction. In some tissue-cells the nucleus is constantly in 

 motion, and according to Haberlandt's investigations, it 

 stops longest where the work of the cell is most pro- 

 nounced for the time being, as for instance in unilateral 

 growth, the formation of hair, local accumulation of 

 chlorophyll, etc. 



This concentration of hereditary characters is most dis- 

 tinctly seen in the sexual cells. Here the other functions 

 are reduced to a minimum. The nucleus dominates com- 

 pletely. In the male sperms the activity of the proto- 

 plasm is limited to moving around and to seeking the fe- 

 male cells. The body is made up almost entirely of the 

 nucleus. In the higher plants the spermatozoids lack even 

 the organs of free motion; they are carried to the egg- 

 cell passively, in the pollen-tubes. The egg-cells are us- 

 ually immovable and heavy in comparison with the male 

 elements, since they contain the food substance necessary 

 for the incipient growth of the germ, and for the first 

 cell-divisions. 



Now fertilization consists in the union of two cells, 

 the male spermatozoid and the female egg-cell. This 

 union is the means of combining the inheritance of the 

 two parents, and therefore the nuclei play the main roles. 

 The nucleus of the egg-cell lies usually in its center; the 

 male nucleus reaches it by passing straight through the 

 surrounding plasm. Sometimes on.e sees quite distinctly 

 that it no longer needs its own protoplasm since it strips 

 it off and leaves it at the border of the egg-cell. In the 

 Cycadaceae, in which the spermatozoa are just large 



