558 PHANEROGAMS. 



frequently partially obscured at a subsequent period by bilateral development and 

 abortion. 



'The Floral Envelope or Perianth is only rarely entirely wanting, as in the 

 Piperaceae and many Aroideoe ; more often it is simple, i. e. it consists of only 

 one whorl of two, three, four, five, or rarely a larger number of leaves (as in 

 Figs. 357, 358) ; in this case the perianth is frequently inconspicuous and composed 

 of small green leaves, as in the Chenopodiaceae and Urticaceae, but is sometimes 

 large, of delicate structure and brightly coloured (petaloid), as in Aristolochia, 

 Mtrabtlis, &c. But in both classes of Angiosperms (Monocotyledons and Dicoty- 

 ledons) the perianth is usually composed of two alternating whorls consisting of the 

 same number of leaves, two, three, four, five, or rarely more. In most Dicotyledons 

 and many Monocotyledons the form and structure of these two whorls is very 

 different ; the outer whorl or Calyx consisting of stouter, green, usually smaller leaves 

 {Sepals), while the inner whorl or Corolla is more delicate, and is formed of white or 

 bright-coloured, usually larger leaves (Petals). It is however more convenient, for 

 the sake of brevity, as Payer has already suggested, to designate the inner whorl as 

 corolla, the outer whorl as calyx, even in those cases where the structure of the two 

 is the same ^ ; and this is the more necessary since the contrast of structure 

 referred to is frequently wanting, both whorls being either sepaloid, as in Jun- 

 caceae, or both petaloid, as in Lilium ; in Helleborus, Aconiium, and some other 

 species, the outer whorl or calyx alone is petaloid, the inner whorl or corolla 

 being transformed into nectaries. In some Dicotyledons the perianth does not 

 consist of alternating whorls, but of a smaller or larger number of turns of spirally 

 arranged leaves, the number of which is then usually large or indefinite ; the outer 

 or lower leaves of this spiral arrangement may in this case also be sepaloid, the inner 

 ones alone petaloid {e.g. Opuntia), or they may all be petaloid (as in Epiphyllum 

 and Trollius), or a gradual transition takes place from the sepaloid through the 

 petaloid to the staminal structure (as in Nymphcea). 



But besides the usual sepaloid and petaloid form and structure of the perianth- 

 leaves, there occur other considerable deviations from the ordinary foliar structure. 

 Thus, for example, the (imperfect) perianth of Grasses consists of very small delicate 

 colourless membranous scales (the Lodicules), that of some Cyperaceae is replaced by 

 hair-like bristles, the SetcB ; in the place of the calyx of Compositae a crown of 

 hairs, the Pappus, surrounds the corolla ; and it has already been mentioned that the 

 petals of Aconitum, Helleborus, &.c. are transformed into nectaries of a peculiar 

 form. 



Whether the perianth consist of one or two whorls, the leaves of the same 

 whorl have very commonly the appearance of being coherent or of coalescing with 

 one another, forming a cup, bell, tube, and so forth, the number of the coherent 

 sepals or petals being determined by that of the marginal teeth. Coherent perianth- 

 whorls are produced, after the formation of the distinct foliar structures at the cir- 

 cumference of the receptacle, by the common zone of insertion of these distinct 

 structures being raised up by intercalary growth as an annular wall, and forming, as 



^ The substantives calyx and corolla then designate the position of the whorl, the adjectives 

 sepaloid and petaloid the nature of the part. 



