m 
COROLLA. 
hesion of the petals ; tne two upper ones form the upper lip, and 
three j)etals cohering in the same manner, form the lower lip. 
Y3. Polypetalous corollas are of various forms, as follows : 
Cruciform^ consisting of four petals of equal size, spreading 
out in the form of a cross, as the radish, cabbage, &c. (Fig. Y9). 
Caryophyllous^ having five single petals, each terminating in a 
long claw, inclosed in a tubular calyx, as the pink (Fig. 80). 
Liliaceous^ with six petals, spreading gradually from the base, 
so as to exhibit a bell-form appearance, as in the tulip and lily 
Fig. 77. Fig. 78. Fig. 79. Fig. 80. Fig. 81. 
Mosaceous^ formed of roundish spreading petals, without claws, 
or with very short ones, as the rose and apple. Pajnlionace' 
ous ; the name is derived from the word papilio^ a butterfly, 
on account of a supposed resemblance in form, as the pea-blos- 
som (Fig. 81). This is an irregula/r polypetalous coroWsi it has 
five petals ; the upper and largest is called the hanner {vexillwn)^ 
the two lateral ones are the wings {al(E\ and the two lower ones, 
cohering by their lower margins so as to form a single piece, are 
called the keel {carina). Among irregular polypetalous corollas 
may be included the orchidaceous^^ which are spurred, hooded, 
(fee, presenting many anomalous forms. 
1 4. The odor of flowers has its origin in the volatile oils, 
elaborated by the corolla ; its production results from causes 
both external and internal, but in both cases equally beyond 
our observation. Temperature renders the odor of flowers 
more or less sensible : if the heat is powerful, it dissipates the 
volatile oils more rapidly than they are renewed ; if the heat is 
feeble, the volatile oils remain concentrated in the little cells 
where they were elaborated ; under these circumstances the 
flowers appear to possess but little odor. But if the heat be 
neither too great nor too little, the volatile oils exhale without 
being dissipated, forming a perfumed atmosphere around the 
flowers. 
a. We perceive the reason, that when we walk in a flower-garden in the morn- 
ing: o»- evening, the flowers seem more fragrant than in the middle of the day ; the 
air being then more charged with humidity, is anotlier cause of an increase of fi-a- 
grance ; as the moisture, by penetrating the delicate tissue of the corollas, expels 
the volatile oils. There are some exceptions to the laws just stated ; for some 
flowers are only odorous during the night, and others during the day. Some flow- 
frs exhale fetid odors, which attract such insects as are usually nourished by putrid 
73. Forms of polypetalous corollas.— 74. Odor of flowers— a. When flowers are most 'ra^rail — Oc «* 
•uinetimes disagreeable. 
