NUCLEUS AND CYTOPLASM 



Their multiplication underlies both kinds of reproduction. In all 

 higher organisms these cells contain a dense spherical body, the 

 nucleus, lying in the more fluid cell substance or cytoplasm. The 

 nucleus has two primarily significant properties. In the first place 

 it can be derived only from a pre-existing nucleus. It has the character 



ACETABULARIA 



CREN MEDN + CRENN->INT CREN/MEDN^MED MED/CRENN_>CREN 



I. — Diagram showing the forms produced by reciprocal grafting of the uni- 



MED 



Fig 



cellular algae Acetabularia mediterranea and crenulata. Where both nuclei are present 

 the hat is regenerated in an intermediate form as if the plant were a sexual hybrid. 

 Where the nucleus is of one species (indicated by N) its influence gradually pre- 

 dominates over the cytoplasm of the stem in regeneration (based on Hammerling 

 1943). 



of heredity in itself. In the second place without a nucleus, or even 

 sometimes with one if it is from a different species, cells die. Bu 

 sometimes a nucleus of one species can be put into a cell of another. 

 This can be done by transplantation in a green alga Acetabularia, 

 whose single cell consists of three parts, hat, stem and base containing 

 the single nucleus. When the stem of one species is grafted onto the 

 base of another and the hat cut off, the new hat that grows is most 

 like that of the species from which the base with the nucleus is taken. 

 This, and similar experiments with various combinations of stem 



Eltments of Genetics 



17 



