94 BOTANY. 
centrifugally. The simplest form is that of a single terminal flower. We 
may suppose a leaf to be developed on each side of the flower, in each of 
whose axils a new bud is produced, which, in turn, may each form the 
centre of a tertiary development, &c. Each flower may be the centre of a 
system of three or more instead of two. If we suppose the leaves above- 
mentioned to be reduced to bracts, the whole forms a single inflorescence, 
called a cyme, this being called dichotomous or trichotomous, according to 
the character of the subdivisions. Occasionally, in dichotomous divisions, 
the flowers are developed on one side only, from which results a pecatiag cur- 
vature of the cyme, which is here called helicoidal, or gyrate. 
As already remarked, the flower, except when terminal, always arises in 
the axil of a leaf, called the bract. Leaves which arise along the floral axis 
are called bracteoles, or bractlets. The true bract may be variously modified 
as to color, shape, &c. At the base of the general umbel, in umbelliferous 
plants, there is a whorl of bracts, termed the general involucre, that at the 
base of the smaller umbels being called the partial involucre or involucel. 
The cup of the acorn is produced by the union of many whorls of bracts. <A 
sheathing bract inclosing one or more flowers is called a spathe. The outer 
sterile bracts in grasses are called glumes. 
b. The Flower and its Appendages. 
The flower consists of whorled leaves placed on an axis, the internodes 
of which are not developed. ‘This shortened axis is the thalamus, or torus. 
There are usually four of such whorls: first, an outer one called the calyz ; 
next, the corolla ; then, the stamens ; and innermost of all, the pistil or 
pistils. Each of these whorls consists, normally, of several parts. The 
plant is called dichlamydeous, when the two outer whorls or the floral envel- 
opes are present ; monochlamydcous, when one only exists ; achlamydeous, 
when neither is present. In most instances the calyx and corolla, when pres- 
ent, are readily detected ; in cases of doubt as to the true character of the 
envelope, or when there is no convenient distinction between the two, the term 
perianth, or perigone, may be employed. Should but one envelope be pres- 
ent, it is always the calyx. 
The manner in which the floral envelopes are folded together is known 
as the estivation, or prefloration. This is valvate, when the elements are 
so arranged as to constitute a circle without the overlapping of the edges. 
Should the edges of the parts be turned outwards, the estivation is 
reduplicate ; if inwards, induplicate. When each part of the whorl overlaps 
the one next to it on one side, and is in turn overlapped by the part on the 
other side, the zstivation is twisted or contorted. Sometimes the elements 
of the whorls, instead of being nearly in the same plane, stand at different 
heights, causing an imbricated estivation. Should the parts envelope each 
other completely, a convolute zstivation is produced. Vevrillary estivation 
is where one part, the vexillum of a papilionaceous flower, envelopes all the 
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