424 GLOSSARY 



Pan'creas (Gr. pan, all ; kreas, flesh) : a digestive gland. It secretes pan- 

 creatic juice. 



Pap'pus : a downy or fluffy outgrowth from the ovary wall. 



Par'asite : an organism which secures its living directly from another living 

 organism without giving anything in return, 



Pas'teurize (from Pasteur the scientist, p. 408) : to heat milk to about 140° 

 Fahrenheit for about 20 minutes for the purpose of killing bacteria in it. 



Pathogenic organisms : bacteria or protozoa which cause disease. 



Pec'toral girdle (Lat. pectoralis, pertaining to the breast) : bones which sup- 

 port the anterior pair of appendages in vertebrates. 



Pel'vic girdle (Lat. pelvis, a basin) : the bony arch to which the posterior 

 pair of appendages are attached in vertebrates. 



Peristal'tic (Gr. peristellein, to surround) : wavelike movements of the muscles 

 of the food tube. 



Pet'al : one of the leaflike parts of the corolla. 



Pet'iole (Lat. petiolus, a little foot) : the stalk of a leaf. 



Phag'ocyte (Gr. phagein, to eat ; kytos, cell) : a colorless corpuscle which de- 

 stroys bacteria. 



Phar'ynx (Gr. pharynx, gullet) : an irregular cavity at the back of the mouth. 



Phloem : that part of the fibrovascular bundle which contains the sieve tubes. 



Photosyn'thesis (Gr. phos, light; synthesis, a putting together) : the pro- 

 cess of making starch out of carbon dioxide and water by the aid of sun- 

 light, as is done by a green cell. 



Photot'ropism : reaction to light. 



Phylum : a large division of the plant or the animal kingdom. It is com- 

 posed of classes. 



Physiological division of labor : performance of different kinds of work by 

 different parts of an organism. 



Physiorogy (Gr. physis, nature ; logos, discourse) : study of the functions 

 of plants and animals. 



Pislil: a structure in the flower containing the ovary, in which the seeds 

 are formed. 



Pith : the soft, spongy tissue in the center of a dicotyledonous stem and be- 

 tween the vascular bundles of a monocotyledonous stem. 



Placen'ta (Lat., placenta, cake) : absorbing organ which nourishes the embryo. 



Plank'ton : small plants a^d animals which live near the surface of bodies of 

 water. 



Plas'ma (Gr. plasma, anything formed or molded) : the colorless fluid part 

 of blood. 



Pleu'ra (Gr. pleura, the side) : the membrane which covers the lungs and 

 lines the cavity containing them. 



Plu'mule : the part of the embryo above the cotyledons which develops into 

 the stem and leaves. 



Pollen grain : a structure in flowers which contains the sperm cell or male 

 gamete. 



