What’s be­hind dif­fer­ent flo­ral scents

The Progress-Index - At Home - - NEWS - BY LEE RE­ICH

Wave af­ter wave of scent has filled the air since my gar­den awak­ened in spring. Most prom­i­nent have been the aro­mas from daf­fodil blos­soms, plum, flow­er­ing cur­rant, and now dame’s rocket, pinks and roses.

Of course, it’s not for us that flow­ers waft those some­times de­lec­ta­ble aro­mas. Evo­lu­tion­ar­ily speak­ing, we don’t re­turn the fa­vor with any­thing more than the car­bon diox­ide that we — and all other an­i­mals — breathe out, and that plants use for pho­to­syn­the­sis.

Flow­ers re­lease their aro­mas to at­tract pol­li­na­tors. As such, flo­ral aro­mas might mimic count­less other kinds of aro­mas, depend­ing on just what crea­ture a par­tic­u­lar flower is try­ing to at­tract.

Some of those flo­ral aro­mas are ac­tu­ally un­pleas­ant to us. Skunk cab­bage (smelly and ined­i­ble) is a good ex­am­ple, but there are worse — or bet­ter — ex­am­ples. The arum lily of South Africa, for ex­am­ple: From its spathe, a spike-like in­flo­res­cence of many small flow­ers ris­ing up from what looks like an up­ended pur­ple skirt, wafts the smell of rot­ting flesh. This aroma is per­fect for at­tract­ing the car­rion bee­tles that pol­li­nate this plant. Heat gen­er­ated in­side the in­flo­res­cence height­ens the mor­bid ef­fect and helps pump the aroma out into the at­mos­phere.

But on to more pleas­ant aro­mas — for in­stance, flow­ers that mimic pheromones, the scents that fe­male an­i­mals give off to sig­nal their readi­ness to mate. Of course, those er­satz pheromones com­ing from flow­ers are di­rected at in­sects, be­cause they are the ones flow­ers want to at­tract to per­form pol­li­na­tion.

Flo­ral de­cep­tion

More than mere scent may be needed to keep an in­sect on a flower. The mir­ror orchid, for ex­am­ple, de­ceives the male bees that pol­li­nate it by not only smelling like re­cep­tive fe­male bees, but also by look­ing like them.

Af­ter one or two flow­ers, any smart bee is go­ing to re­al­ize that he’s not deal­ing with a real fe­male and give up try­ing. So to keep up the de­cep­tion, each mir­ror orchid plant smells slightly dif­fer­ent; it takes a half dozen or so be­fore a bee catches on, and by then the flow­ers have got­ten what they wanted.

Even more in­tri­cate in its de­cep­tion is the bucket orchid of Cen­tral Amer­ica, which splays out lit­tle “buck­ets” filled with a quar­ter-inch of perfumed liq­uid. Each of the 20 or so species of this plant has a slightly dif­fer­ent per­fume — al­though the dif­fer­ences are un­de­tectable to us — ac­cord­ing to the species of iri­des­cent bee it means to at­tract. In the flurry of ac­tiv­ity around a bucket, an oc­ca­sional bee falls in. As the bee squeezes out through a nar­row tube, it in­ci­den­tally pol­li­nates the orchid flower.

Aro­mas that please hu­mans

What makes a scent pleas­ing to hu­mans? Per­haps, as with bees, some aro­mas con­jure up pleas­ant primeval as­so­ci­a­tions. At any rate, we like them enough to put great ef­fort into cap­tur­ing and bot­tling them.

The first es­sen­tial oil, at­tar of rose, was bot­tled by the Ara­bian physi­cian Avi­cenna about 1,000 years ago. Two hun­dred years later, Eleanor of Aquitaine had 2,500 pounds of vi­o­lets crushed to make 1 pound of vi­o­let at­tar.

Hu­mans soon learned to pre­serve a scent bet­ter by com­bin­ing it with a fix­a­tive. Fix­a­tives orig­i­nally were musk ex­tracted from the gen­i­tal area of deer and am­ber­gris from sperm whales, but now syn­thet­ics are also used.

As an al­ter­na­tive to the elab­o­rate ex­trac­tion and fix­ing of flo­ral aro­mas, con­sider plant­ing a rose out­side your back door, then step­ping out­side and putting your nose to it. Even bet­ter, plant a spec­trum of scented blos­soms for sen­sory thrills from late win­ter to late fall.

AP PHOTO

In this un­dated photo, strong fra­grance in ad­di­tion to beau­ti­ful blos­soms dou­ble the plea­sure of Straw­berry Hill rose, from rose breeder David Austin, in New Paltz, New York.

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