GLOSSARY 157 



Germ-cell. A reproductive cell, which, usually after union with 

 a germ-cell from another individual (fertilisation), develops 

 into a new individual. In animals the germ-cells of the male 

 are spermatozoa, those of the female ova (egg-cells). In 

 plants the male germ-cells are contained in the pollen ; the 

 female, egg-cells, in the ovules or embryo-seeds. 



Germ-plasm. The germinal substance, which according to 

 Weismann is alone able to give origin to new individuals. 



Heterozygote. An individual containing both members of an 

 allelomorphic pair of characters, i.e. which is hybrid in respect 

 of that pair of characters, and produces germ-cells bearing 

 one and the other respectively. Adjective heterozygous. 



Homozygote. An individual made by union of two germ-cells 

 each of which bears the same member of an allelomorphic 

 pair of characters, so that it is ' pure ' in respect of that 

 character, and all its germ-cells bear the same character. 

 Adj ective homozygo us. 



Mode. The most frequent condition of a character which varies 

 continuously. Its measurement is called the modal value. 



Mutation. A variety which is not connected with the type by 

 intermediates. More strictly, the sudden origin of such a 

 variety. 



Nucleus. A sharply defined body found in every cell, which seems 

 to control the activities of the cell. 



Ovum. The germ-cell produced by the female, an egg-cell. 



Pin-eye. In Primula (Primrose, Cowslip, etc.), the form in 

 which the style is long and the anthers low down in the 

 flower-tube. The other form, with short style and anthers 

 high up, is called Thrum-eye. 



Pollen. The powder bearing the male germ-cells in a flowering 

 plant. 



Polymorphism. The condition in which a species exists in 

 several distinct forms or varieties. 



Recessive. When two individuals are crossed, bearing different 



