GLOSSARY 619 
Non-cross-over Gamete.—A gamete containing a chromosome which has not 
been affected by crossing-over. 
Non-disjunction.—The failure of the two members of a pair of homologous chromo- 
somes to disjoin in the reduction division so that both pass into the same gamete. 
Normal Allelomorphs.—The factors conditioning the characters of the wild or 
normal type of a species as contrasted with the factors which condition mutant 
characters. 
Nucleoplasm.—The protoplasm in the nucleus. 
Nucleus.—The more or less centrally situated cell organ containing the chro- 
matin which has come to be known as the hereditary substance par excellence. 
Ontogeny.—The development of the individual as opposed to phylogeny. 
Ovules.—The macrosporangia of flowering plants; the female sex cells with the 
immediately surrounding parts; the future seeds. 
Paramecium.—A ciliated protozoan. 
Pedigree.—List of ancestors; genealogical tree. 
Peloric Flowers.—Regular flowers borne on plants which normally have irregular 
flowers. 
Pericarp.—In flowering plants the seed vessel or ripened ovary; in maize each 
seed is morphologically a fruit and the seed covering is termed pericarp. 
Petiole.—Leaf stalk. 
Phenotype.—The sum of the externally obvious characters of an individual or a 
group of individuals. 
Phyletic.—Pertaining to ancestral species or groups. 
Phylogeny.—The history of the evolution of a species or group; distinguished 
from ontogeny. 
Phylloxera.—A genus of plant lice; usually of gall-making habits. 
Phylum (pl. Phyla).—A primary division or sub-kingdom of the animal or vege- 
table kingdom. 
Physiology.—The sum of scientific knowledge concerning the functions of living 
things. 
Phytomer—A plant-part or plant-unit; one of the structures or elements 
which, produced in a series, make up a plant of the higher grade. The ultimate 
similiar parts into which a plant may be analyzed are units consisting of an inter- 
node and a node with its leaves. Each unit may reproduce its like or the entire 
plant. 
Polled.—Hornless. ? 
Pollen.—The male sex cells of flowering plants. 
Polydactylous.—Having extra fingers or toes. 
Polyphyletic.—Derived from several phyla; having several different lines of descent. 
Prepotent.—Able to impress individual characteristics upon offspring to a marked 
degree. 
Probable Error.—An arbitrary term used to designate the amount that must be 
added to or subtracted from the observed value to obtain two limiting figures of 
which it may be said that there is an even chance that the true value lies within or 
without these limits. 
Protein.—Complex organic substances containing nitrogen, e. g., albumin or white 
of egg. 
Pure Line.—A group of individuals derived solely by one or more self-fertilizations 
from a common homozygous ancestor. Sometimes erroneously applied to groups of 
individuals believed to be genotypically homogeneous (a homozygous biotype or a 
clone) without regard to their method of reproduction. 
Quagga.—A zebra-like animal from South Africa. Named from the sound of its cry. 
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