GLOSSARY. 495 



Ontogeny. The life-history and modification of a single, or 

 individual, organism. The history of an individual as dis- 

 tinguished from that of the race. See Phylogeny. Ontogeny 

 is development. 



Organ. A part of an organized body directly associated with 

 the vital functions, as the heart and lungs of animals. 

 Compare Member. In plants, many parts are at once both 

 organs and members, as the leaves ; when one is consider- 

 ing these parts from the standpoint of morphology, or form, 

 it is proper to speak of them as members, but from the 

 standpoint of function or use, they may be spoken of as 

 organs. 



Organism. A body exhibiting life. An animal or a plant of 

 any kind or description. Used as a generic term to desig- 

 nate all forms of life. 



Pangenesis. A mechanical theory of the means or vehicle of 

 heredity, proposed by Darwin, which supposes that every 

 part or unit of the corporeal structure is represented in the 

 germ by minute gemnmles thrown off from itself. (Page 60.) 



Panmixia. A term used by Weismann to designate the agency 

 of modification or evolution which results from the cessation 

 of natural selection. "But as soon as an organ becomes 

 useless, the continued selection of individuals in which it is 

 best developed must cease, and a process which I have 

 termed panmixia takes place." — Weismann. (Page 29.) 



Phylogenetic. Pertaining to the racial history or evolution of 

 any tribe or group of organisms. 



Phylogeny. The tribal or ancestral history and modification of 

 organisms. The natural history of the race, as distinct from 

 that of the individual. See Ontogeny. Phylogeny is the 

 material of evolution. 



Phylum (plural, p/ii/ta). A line of ascent. The stem or main 

 direction of the evolution of any given tribe. A genealogy. 



Phyton, Phytomer. That portion of any plant which, when 

 removed and treated as a cutting or a graft, may produce 

 a new plant. It is usually a bud, node, and internode. 

 (Pages 72, 84.) 



Plasm, Plasma. The assumed fundamental, undifferentiated 



