72 
COROLLA. 
5th. Papilionaceous^ a flower with a 
banner, two winss, and a keel; the 
name is derived ^om the word papi- 
lio, a butterfly, on account of a sup- 
posed resemblance in form, as the 
pea-blossom, Fig. 78. 
If a corolla is not, in form, like any 
of those we have described, it is said 
to be anomalous. 
Odour of Flowers. 
The odour of flowers has its origin in the volatfle oils, elaborated 
by the corolla ; its production results from causes both external and 
internal, but, in both cases, equally beyond our observation. Tem- 
perature renders the odour 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 very feeble, the volatile oils remain con- 
centrated in the little cells where they were elaborated ; under these 
circumstances the flowers appear to possess but little odour. But 
if the heat is neither too great nor too little, the volatile oils exhale 
without being dissipated, forming a perfumed atmosphere around 
the flowers. 
You perceive the reason, that when you walk in a flower garden 
in the morning or evening, the flowers seem, more fragrant than in 
the middle of the day. The air being more charged with humidity, 
is another cause of an increase of fragrance at those times ; 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 flowers exhale fetid odours, which attract 
such insects as are usually' nourished by putrid animal substances. 
Many flowers exhale sweet odours ; but, however odours may differ, 
in the sensations which they produce, it is certain, that powerful 
ones have a stupifying, narcotic effect upon the nerves, and that it 
is dangerous to respire, for any great length of time, even the most 
agreeable of them, in a concentrated state. 
One important oflnce of the corolla, is to secure those delicate and 
important organs which it encloses, the stamens and pistils, from 
ill external injury, and to favour their development. After the 
^erm is fertilized by the influence of the pollen, the corolla fades 
iway, and either falls off or remains withered upon the stalk ; the 
viices which nourished it then go to the germ., to assist in its growth, 
nd enable it to become a perfect fruit. 
Another use of the corolla seems to be, to furnish a resting-place 
Tor insects in search of honey. 
The corolla is supposed by Darwin to answer the same purpose 
' to the stamen and pistils, as the lungs in the animal system ; each 
petal being furnished with an artery which conveys the vegetable 
blood to its extremities, exposing it to the light and air under a 
delicate moist membrane ; this vegetable blood, according to his 
theory, is then collected and returned in correspondent veins, for 
Papilionaceous — What corollas are anomalous?— Origin of the odoiir of flowers — 
Odour affected by temperature— Odour affected by moisture— Odours so iietimes dis- 
agreeable—Dangerous if respired for a long time — Ofl&ce of the corolla — Darwin's 
theory with, respect to the corolla. 
