Petal 



One of the parts of the Corolla of a flower. 



Petiole 



The stalk of a leaf. 



Petran 



Refers to the Rocky Mountains. 



Petrification 



The formation of fossils by the replacement of organic 

 substances in dead organisms by minerals. 



P* 



A measure of the energy by which a soil holds water; 

 soil dried at 100-110 C has a pF of 7.0, the tension de- 

 creases as the water content increases. 



pH 



A measure of the acidity or alkalinity of a solution, or 

 the concentration of H or OH ions, ranging from to 14. 

 Values above 7 are alkaline, below 7 are acid. cf. Reaction 

 (2). 



Phoge 



See Bacteriophage. 



Phagocyte 



A cell that engulfs bacteria or other particles, e. g., white 

 corpuscles in the blood. 



Phagocytosis 



The engulfing of particles by a Phagocyte. 



Phanerogam 



See Spermatophytes. 



Phanerophyte 



One of Raunkiaer*s life-form classes (q. v.) in which the 

 buds or other perennating parts are more than 25 cm. above 

 the ground, especially trees and shrubs. 



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