Nectar: a sweetish substance in blossoms of flowers from which bees make honey.
Nitrate: a readily usable form of nitrogen. The most common nitrate is saltpeter.
Nitrogen: a chemical element, one of the most important and most expensive plant foods. It exists in fertilizers, in ammonia, in nitrates, and in organic matter.
Nodule: a little knot or bump.
Nutrient: any substance which nourishes or promotes growth.
Organic matter: substances made through the growth of plants or animals.
Ovary: the particular part of the pistil that bears the immature seed.
Ovipositor: the organ with which an insect deposits its eggs.
Oxygen: a gas present in the air and necessary to breathing.
Particle: any very small part of a body.