ANGIOSPERMS. 
537 
peculiar structure, sharply differentiated as a whole from the rest of the organism. 
This peculiar appearance is due not only to the special properties of its axis, 
but especially to the presence of the floral envelopes, and most of all to the 
circumstance that the foliar structures of the flower are arranged, with rare 
exceptions, in the form of whorls, even when the leaves of the vegetative shoots 
are alternate or distichous, or disposed in other similar arrangements. Each of 
the distinct appendicular organs of the flower, viz. the perianth, androecium, and 
gynaeceum, is usually represented by several members arranged in concentric 
circles or in a spiral ; so that one or more perianth-whorls are immediately succeeded 
within by one or more whorls of stamens, and these by the gynaeceum in the 
centre of the flower. One or other of these whorls may however be absent, or 
each of the separate whorls may be represented by only a single member, as 
Fig. ^(^Q.—Hippnris vulgaris ; A piece of an erect stem, the flowers standing in the axils of the whorl of leaves (whicli have 
been cut off) ; B horizontal section of a female flower above the ovary, p perianth, cp carpel ; C horizontal section of the anther ; 
I— IV longitudinal section of flowers in various stages of development, a anther, f filament, g style, n stigma, / perianth, 
fk the inferior ovary, sk the pendulous and anatropous ovule. 
in Hippuris (Fig. 360), where only one stamen and one carpel are contained within 
a scantily developed perianth. It is only rarely that the whole flower is reduced 
to a single sexual organ, as the female flowers of Piperaceae, or the male and 
female flowers of some Aroidese ; it is much more commonly the case that the 
flower is composed of successive whorls of members disposed from without inwards 
(or from below upwards), consisting of the same or multiples of the same number ^, 
radiating from the centre on all sides like a rosette, an arrangement which is 
^ [To this peculiarity of structure the term ' symmetrical ' is generally applied in English text- 
books; in the present v/ork however this word is used in a very different sense, namely in reference to 
any structure (foliar or floral) which can be divided into two similar halves, or the parts of which are 
radially disposed around a central point; see p. 204.] 
