414 BIOLOGY 



pigment cells (Lat. pingere = to paint). Cells which contain coloring 



matter, 176. 

 pineal gland. A small body lying on top of the brain; also called the pineal 



eye; same as epiphysis, 193. 



pistil. The central row of leaves (carpels) of a flower, bearing female re- 

 productive organs; also called the gyncecium, 120. 



pith. The central mass of cells in a stem, made of fundamental cells, 104. 

 pituitary body. A small body on the under side of the brain; the hypophy- 

 sis, 193. 



placenta. The membrane by which the embryo is attached to the uterus 

 in mammals, 291; in plants, the line of attachment of seeds in the 

 ovary, 

 plankton (Gr. plankton = wandering). The living organisms which float 



in water, largely microscopic. 



plantigrade. Walking on the palms of the hands or the soles of the feet, 

 plasma. The liquid portion of circulating blood, 191, 205. 

 plasmodium (Gr. plasma = substance). A jelly-like mass. 

 Plasmodium malarice, 69, 239. 

 plastids. Miscellaneous bodies within a cell, 37. 

 platelets. Minute bodies in the blood of vertebrates, 192. 

 pleura (Gr. pleura = a rib). Membranes surrounding the lungs. . 



Pleurococcus, 77, 239. 



plexus (Lat. pleclare = to weave). A network of nerves, 194. 

 pneumogastric (Gr. pneumon = lung + gaster = stomach). A large, cere- 

 bral nerve extending down the neck and supplying the heart, lungs, and 

 stomach, 194. 

 Podocoryne, 277. 

 poisons. Substances which, taken into the body, produce injurious effects, 



43. 



polar cells. Small cells extruded from the egg during its maturation, 254. 

 pollen. The male spores produced by a flower, 119. 

 pollen tube. An outgrowth from a pollen grain which pushes through the 



style of a flower to fertilize the egg in the ovary, 122, 275. 

 poll ex. The thumb. 



pollination. The transfer of the pollen to the stigma, 277. 

 polygamous (Gr. polus = many + gamos = marriage). The sexual asso- 

 ciation of one male with several females, 

 polymorphism (Gr. polus = many + morphe = form). The property of 



having two or more forms of the same animal, 149. 

 portal circulation. The circulation of blood from the intestine through the 



liver; it has two capillary systems, 190. 

 portal vein. The vein carrying blood from the intestine to the liver, 190. 



