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360 naked seed not only this kind of fruit, but every monospermous pericarpinm bearing a general resemblance to a seed, and whose outer covering, though distinct from the nucleus, is only ruptured after germination commences.

For the purposes of an artificial arrangement this language may perhaps be sufficiently accurate; but in determining the affinities of plants, it is necessary to express by appropriate terms those differences which are no less important than real.

Of the fruits improperly called naked seeds, there are two principal kinds: the first, in which the pericarpium is distinct from the seed, is termed Akena by Richard in his excellent Analyse du Fruit; the second, in which the pericarpium coheres with the seed, is the Caryopsis of the same author.

An Akena (or Achenium), even in a separate state, may in general be readily determined. But it is not always equally easy to distinguish a Caryopsis from a seed. It may indeed be done in certain cases, as in Grasses, by attending to its surface, in which two distinct and distant cicatrices are observable; the one indicating the point of attachment to the parent plant, the other that by which it was fecundated. In certain other tribes, however, this criterion cannot be had recourse to, the surface of the Cariyopsis exhibiting but one areola or cicatrix, which includes the closely approximated points of attachment and impregnation: in such cases, the true nature of the fruit can only be determined by its examination in an earlier stage.

But although it must be admitted that an ovulum is never produced without a covering, through some part of $145]$ which it is impregnated; it is still possible to conceive a case in which a ripe seed may be considered as truly naked while retaining its attachment to the parent plant; and this not subsequent to germination, but even preceding the formation of the embryo. For if we suppose, as the immediate effect of impregnation, a swelling of the ovulum without a corresponding enlargement of the ovarium, the consequence will obviously be a premature rupture of the ovarium, and the production of a seed provided with its proper integuments only.