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igneous— Said of a rock or mineral solidified from molten or partly molten material (a magma).

incisor— One of a set of cutting-adapted teeth at the front of the jaw.

inflected— Refers to songs or calls of birds characterized by a change in pitch or loudness.

inflected slurs— Bird calls or songs that smoothly change in pitch.

inflorescence— The disposition of flowers on an axis; the flower arrangement on a plant. (See Fig. 6.1.)

insectivorous— Insect-eating.

inselberg— An isolated residual knob or hill rising abruptly from a lowland erosion surface, especially in desert regions. It is characteristic of a late stage of the erosion cycle.

instar— The stage between moults of a larval or nymphal insect.

interfluve— The relatively undissected upland or ridge between adjacent streams flowing in the same general direction.

internasal scales— Scales between the nostrils.

internode— The portion of a stem between nodes. (See Fig. 6.1.)

introduced— Refers to a plant or animal brought in deliberately by man and growing in the area without cultivation. For example, an introduced fish may be "exotic" (from a foreign land) or "transplanted" (outside its native range but still within the country of origin).

intrusive— Pertaining to an intrusion (emplacement of magma in preexisting rock).

involucre— A whorl of bracts subtending a flower cluster, as in the heads of sunflowers. (See Fig. 6.1.)

isotope— One or more species of the same chemical element that vary in the number of neutrons in the nucleus.