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With free spores Exospore�     b.

The exospore is sometimes roughened, with more or less projecting warts, as may be seen in Russula, which much resembles Lactarius in this as in some other particulars.

Sometimes the exospore is ruptured and detached loosely from the germinating spore.

Some mycologists are of opinion that the covering of the spore is double, consisting of an exospore and an endospore, the latter being very fine and delicate.

The mature pollen-grain is, like other spores, a single cell; except in the case of some submerged aquatic plants, it has a double wall, a thin delicate wall of unaltered cellulose, the endospore or intine, and a tough outer cuticularized exospore or extine.