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xvi usually called leaves or segments) is one in which the sepals and petals are similar in form and texture, and present apparently a single whorl. But if examined in the young bud, one half of the parts will generally be found to be placed outside the other half, and here will frequently be some slight difference in texture, size, and colour, indicating to the close observer the presence of both calyx and corolla. Hence much discrepancy in descriptive works. Where one botanist describes a simple perianth of six segments, another will speak of a double perianth of three sepals and three petals.

99. The following terms and prefixes, expressive of the modifications of form and arrangement of the corolla and its petals, are equally applicable to the calyx and its sepals, and to the simple perianth and its segments.

100. The Corolla is said to be monopetalous when the petals are united, either entirely or at the base only, into a cup, tube, or ring ; polypetalous when they are all free from the base. These expressions, established by a long usage, are not strictly correct, for monopetalous (consisting of a single petal) should apply rather to a corolla really reduced to a single petal, which would then be on one side of the axis ; and polypetalous is sometimes used more appropriately for a corolla with an indefinite number of petals. Some modern botanists have therefore proposed the term gamopetalous for the corolla with united petals, and dialypetalous for that with free petals ; but the old established expressions are still the most generally used.

101. When the petals are partially united, the lower entire portion of the corolla is called the tube, whatever be its shape, and the free portions of the petals are called the teeth, lobes, or segments (39), according as they are short or long in proportion to the whole length of the corolla. When the tube is excessively short, the petals appear at first sight free, but their slight union at the base must be carefully attended to, being of importance in classification.

102. The Æstivation of a corolla, is the arrangement of the petals, or of such portion of them as is free, in the unexpanded bud. It is

valvate, when they are strictly whorled in their whole length, their edges being placed against each other without overlapping. If the edges are much inflexed, the æstivation is at the same time induplicate ; involute, if the margins are rolled inward ; reduplicate, if the margins project outwards into salient angles ; revolute, if the margins are rolled outwards ; plicate, if the petals are folded in longitudinal plaits.

imbricate, when the whorl is more or less broken by some of the petals being outside the others, or by their overlapping each other at least at the top. Five-petaled imbricate corollas are quincuncially imbricate when one petal is outside, and an adjoining one wholly inside, the three others intermediate and overlapping on one side ; bilabiate, when two adjoining ones are inside or outside the three others. Imbricate petals are described as crumpled (corrugate) when puckered irregularly in the bud.

twisted, contorted, or convolute, when each petal overlaps an adjoining one on one side, and is overlapped by the other adjoining one on the other side. Some botanists include the twisted æstivation in the general term imbricate ; others carefully distinguish the one from the other.

103. In a few cases the overlapping is so slight that the three æstivations cannot easily be distinguished one from the other ; in a few others the æstivation is variable, even in the same species, but, in general, it supplies a constant character in species, in genera, or even in Natural Orders.

104. In general shape the Corolla is tubular, when the whole or the greater part of it is in the form of a tube or cylinder. campanulate, when approaching in some measure the shape of a cup or bell.

urceolate, when the tube is swollen or nearly globular, contracted at the top, and slightly expanded again in a narrow rim.

rotate or stellate, when the petals or lobes are spread out horizontally from the base, or nearly so, like a wheel or star.

hypocrateriform or salver shaped, when the lower part is cylindrical and the upper portion expanded horizontally. In this case the name of tube is restricted to the cylindrical part, and the horizontal portion is called the limb, whether it be divided to the base or not. The orifice of the tube is called its mouth or throat.