616 GENETICS IN RELATION TO AGRICULTURE 



Character. One of the many details of structure, form, substance or function 

 which make up an individual organism. 



Chimera. A mixture of tissues of different genetic constitution in the same part 

 of a plant. 



Chlorophyll. The vegetable pigment which gives the characteristic color to ordi- 

 nary green plants. 



Chromatin. The most permanent and characteristic constituent of the nucleus; 

 so called on account of the readiness with which it becomes colored by certain dyes. 



Chromomeres. The chromatin granules, which are sometimes arranged like the 

 beads on a necklace. 



Chromosome. A definite aggregation of chromomeres. 



Cleistogamous Flowers. Those in which development is arrested in the bud but 

 which are fertile. The more perfect flowers of the same plant are often nearly or 

 quite sterile. This peculiar dimorphism is known to occur in about 60 genera. 



Clone. A group of individuals produced from a single original individual by 

 some process of asexual reproduction, such as division, budding, slipping, grafting, 

 parthenogenesis (when unaccompanied by a reduction of the chromosomes), etc. 



Contabescense. An abortive condition of the stamens and of pollen; of very 

 common occurrence in hybrid plants. 



Crossing-over. Exchange of chromatin material between homologous chromo- 

 somes. 



Cross-over Gamete. A gamete containing one or the other of a pair of homologous 

 chromosomes which have interchanged parts by crossing-over. 



Cytology. The branch of biology which treats of cells, especially of their internal 

 structure. 



Cytoplasm. That portion of the protoplasm of the cell outside the nucleus. 



Dam. A female parent, referring to mammals; generally with sire as the male 

 parent. 



Development. The complete process of growth of an individual. 



Differentiation. The process of producing specific parts or substances from a 

 general part or substance. 



Dimorphic. Comprising two distinct forms. 



Dioecious Plants. Those having the two different sexes on different plants, thus 

 insuring cross-fertilization. 



Diploid. The number of chromosomes normally found in the somatic cells of a 

 species; twice the gametic or haploid number. 



Dominant. Applied to one member of an allelomorphic pair, having the quality 

 of manifesting itself wholly or partly to the exclusion of the other member. 



Drosophila. A genus of fruit flies, D. ampelophUa the pomace or fruit fly. 



Embryogeny. Early development of an egg leading to the formation of an 

 embryo. 



Embryology. The science which treats of embryogeny. 



Endosperm. The substance stored in a seed adjacent to the embryo for its early 

 nourishment. 



Epistatic. Applied to a factor or gene which conditions a certain character when 

 present in a genotype which contains a factor or factors in other loci affecting the 

 same character; for example, the factor P for purple aleurone in maize is epistatic 

 to R, the factor for red aleurone; contrasted with hypostatic. 



Equidae. The horse family. 



Equus. The typical genus of the family Equidse. 



Evolution. The general name for the history of the steps by which any living 

 being has derived the morphological and physiological characters which distinguish it. 



