Perennial: living through several years. All trees are perennial.
Petal: a single leaf of the corolla.
Phosphoric acid: an important plant food occurring in bones and rock phosphates.
Pistil: the part of the blossom that contains the immature seeds.
Pollen: the powdery substance borne by the stamen of the flower. It is necessary to seed production.
Pollination: the act of carrying pollen from stamens to pistils. It is usually done by the wind or by insects.
Porosity: the state of having small openings or passages between the particles of matter.
Potash: an important part of plant foods. The chief source of potash is kainit, muriate of potash, sulphate of potash, wood ashes, and cotton-hull ashes.
Propagate: to cause plants or animals to increase in number.
Protein: the name of a group of substances containing nitrogen. It is one of the most important of feeding stuffs.