k 



Pleiotroplsm — 117 — Polygenes 



of the pollen-sac and each gives rise to a pollen tetrad, the 

 individual cells of which develop without further division into 

 pollen grains. 



Pollen-tube. — The protoplasmic tube which grows out from 

 a germinating pollen-grain and penetrates the stigmatic tis- 

 sues passing down the style to fertilize an ovule. 



Pollinate. — To place pollen on a stigma. 



Pollination. — The act of placing pollen on the receptive 

 surface of a stigma. 



Polocyte, or first polar body. — The small degenerate sister 

 cell of the secondary oocyte. This first polar body generally 

 divides into two polar bodies which disintegrate. 



Polyadelphous. — With stamens separate, or in more than 

 two groups. 



Polyallel Crossing. — Crossing each inbred line with every 

 other inbred line, or with certain other inbred lines; an ex- 

 tension of diallel crossing to cover the simultaneous compari- 

 son of more than two sires. 



Polyandrous. — (i) With twenty or more stamens per flower, 

 (ii) having more than one male mate. 



Polyarch. — A type of anastral spindle in higher plants that 

 is multipolar from the beginning (Strasburger; Wilson). 



Polycaryon, Polykaryon. — A polykaryotic individual. 



Polycaryoptic. — Having multiple seed formation. 



Polycaryotic, Polykaryotic. — Having several nuclei in the 

 one cell. 



Polychlamydeous Chimaera. — A periclinal chimaera in 

 which the peripheral constituent is more than two thicknesses 

 of cells. 



Polychronism. — The independent origin of a species at more 

 than one time (Cain, 1944). 



Polyclinal Chimaera. — A chimaera in which more than two 

 components are involved. 



Polyembryony. — The presence of more than one embryo in 

 a seed: often one embryo is sexually produced and the re- 

 mainder vegetatively by diploid parthenogenesis (q.v. under 

 Parthenogenesis) . 



Polygamous. — (i) With both perfect and imperfect flowers 

 present on the same plant, (ii) Of an animal: having more 

 than one mate during one breeding season. N. Polygamy. 



Polygenes. — (i) Linked combinations of the genes determin- 

 ing quantitative variation (Mather), (ii) Minor genes con- 

 trolling quantitative characters which individually have too 

 small an effect to show clear segregation. 



