06 COROLLA. 



hesion of the petals ; the two "upj^er ones form the upper lip, and 

 three petals cohering in the same manner, form the lower lip. 

 73. Polyjyetalous corollas are of varions forms, as follows ; 

 Cruciform^ consisting of fonr petals of eqnal size, spreading 

 ont in the form of a cross, as the radish, cabbage, &c. (Fig. 79). 

 Caryoj)hyllous^ having five single petals, each terminating in a 

 long claw, inclosed in a tnbular calyx, as the j^ink (Fig. 80). 

 Liliaceous^ with six petals, spreading gradually from the base, 

 so as to exhibit a bell-form apj)earance, as in the tulip and lily. 



Fig. 77. Fig. 78. Fig. 79. Fig. 80. Fig. 81. 



Hosaceoiis^ formed of roundish spreading petals, without claws, 

 or with very short ones, as the rose and apple. Papilionace- 

 ous y the name is derived from the word jpajyilio^ a butterfly, 

 on accoimt of a su]3posed resemblance in form, as the pea-blos- 

 som (Fig. 81). This is 2i\ irregula.r polypetalous corolla; it has 

 ^YQ petals ; the upper and largest is called the 'banner {vexillum)^ 

 the two lateral ones are the wings (alce)^ and the two lower ones, 

 cohering by their lower margins so as to form a single piece, are 

 called the Jceel {carina)- Among irregular polypetalous corollas 

 may be included the orc/iidaceous, which are spurred, hooded, 

 &c., presenting many anomalous forms. 



74. The odor of flovm^s 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 

 w^here 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 dissi]3ated, forming a perfumed atmosphere around the 

 flowers. 



a. We perceive the reason, that when we -walk in a flower-garden in the morn- 

 ing or evening, the flowers seem more fragrarti than in the middle of.the day ; the 

 air being then more charged with humidity, is another cause of an increase of fra- 

 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 onjy odorous during the night, and others during the day. Some flow- 

 ers exliale fetid odors, which attract such insects as arc usually nourished by putrid 



73. Forms of polyi)eta!ous corollas, — 74. Odor of flowei-s— a. When flowers are most fragrant — Odors 

 •ometimes disagreeable. 



