A BWCA Glossary


Ichthyoplankton
Freshwater plankton made up of fish eggs, newly hatched eggs (fry), young fish, and adults of small fish. From the Greek, icqus (ichthys), "fish".
Icterid
Any of the New World birds of the family Icteridæ, the Blackbirds and Orioles. Represented in the North Country by three blackbirds, the Red Winged Blackbird (Agelaius phoeniceus), Rusty Blackbird (Euphagus carolinus), and Common Grackle (Quiscalus quiscula), and a feathered nest parasite, the Brown Headed Cowbird (Molothrus ater).
Igneous
Any rock solidified from molten or partly molten material. BWCA basalt, gabbro, and granite are of igneous origin.
Indusium
On a fern, the protective covering for the Sorus, the cluster of spore producing Sporangia. Not present in all species.
Inflorescence
The group or arrangement in which flowers are borne on a plant; the floral structure.
Insectivore
Animal whose diet is made up primarily of insects and other invertebrates. In northern bogs, the insectivores include some plants.
Instar
The stage in an insect's life history between any two moults. A newly-hatched insect which has not yet moulted is said to be a first-instar nymph or larva. The adult is the final instar.
Internode
The portion of a stem between two successive nodes, the gap between successive points of attachment of leaves on a stem.

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Interrupted
Discontinuous; in an inflorescence, having clusters of flowers interspersed with bare areas of stem; in the Interrupted Fern (Osmunda claytonia), having the non-fertile frond broken by the interspersion of the fertile organs.
Interstadial
The lengthy period of warm temperatures between ice ages. Some geologists suspect that we may, in our time, be living in the interstadial which will precede the fifth ice age.
Intrusive
Igneous rock formed beneath the surface of the Earth; typically with large crystals due to slow cooling. Also known as plutonic; opposite of extrusive or volcanic.
Involucre
A whorl of bracts located beneath (subtending) a flower cluster, as in the heads of members of the sunflower family (Asteraceae).
Isinglass
A form of gelatin prepared from the inner lining of the air bladders of fishes, including, at one time, the Lake Sturgeon (Acipenser fulvescens). Sometimes used as a clarifying agent in jellies, glues, wines, and home brew, as well as in the isinglass windows of carriages and early cars.
Island Arc
The belief, supported by geological evidence, that the Superior Uplands were, in Precambrian times, an arc of offshore islands.
Izaak Walton League
Minnesota IWLA involvement with the BWCA began in the 1920’s, and has continued to this day. Minnesota Division members, particularly Miron “Bud” Heinselman, were key players in the arduous battle to preserve the Boundary Waters for future generations. The Compleat Angler (full e-text of Izaak Walton's classic).
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Last Updated on 11 April, 2004