Naturespeak

Sex and the single plant

By Bob Brett,

Whistler Naturalists

" I could be content that we might procreate like trees, without conjunction, or that there were any way to perpetuate the World without this trivial and vulgar way of coition: it is the foolishest act a wise man commits in all his life ."

— Sir Thomas Browne, ca. 1644.

I got the call, but there was something funny about the way she said "your book is in." After rushing to the Whistler Library, I walked to the front counter and boldly asked for it. Eyes averted, Joan scurried over to Suzanne for a fierce whisper. Both watched with faint revulsion as I took the book, carefully wrapped in brown paper. As I left, I’m sure I heard some tsk, tsking from behind.

Yes, I admit it. I am in possession of a book about sex, a great book — The Sex Life of Plants — written by a really funny but slightly demented Brit named Alec Bristow. It’s about the multitude of methods flowers use to reproduce. Better yet, it shows how our puritanical attitude towards sex blinkered us for centuries to what’s so obviously right in front of our eyes.

Can you imagine that it took western civilization until 1694 to discover plant sexuality? Even then, the concept that plants had sexual parts, and that the entire purpose of a flower was sexual reproduction, wasn’t widely accepted until the late 1800s. Most learned people (like the cheery Sir Thomas in the quote above) held to a literal reading of the Bible, and Genesis clearly states that plants were created on the third day — three days before the creation of males and females. Plants, they reasoned, must therefore be sexless (which is why we still imply sexual purity by saying "white as a lily," and call the loss of virginity "deflowering").

But sex has always been on the agenda of plants regardless of human beliefs. And over the millennia, plants have devised a huge array of ways to reproduce sexually. Some plants are wind-pollinated (like cottonwoods and dandelions), but most are pollinated by animals such as bats, birds, bees, and bugs.

Plants attract pollinators mainly through the promise of nectar, usually hidden deep enough in the flower that the pollinator must brush up against the plant’s sexual parts. The animal gets nectar and in exchange the plant gets a delivery service as good as FedEx. Brushing up against the male parts douses the pollinator with pollen. When it then visits the next plant, that pollen is delivered to the female parts and sexual reproduction is achieved.

A plant’s male and female parts are most obvious in a big flower like a wild tiger lily which has six similar projections encircling a single tube. The six projections are stamens (male parts) which produce pollen. The single tube includes the female parts, together called a pistil. The top of the pistil (the style) is sticky and enlarged, all the better to catch pollen. At the bottom of the pistil is an ovary which, like in any mammal or other animal, is an egg container. The pollen (or sperm) sticks to the style, then grows down into the ovary and fertilizes it. The result of the sexual union is a viable seed.

So what is the purpose of sex, anyway? Surely all the complex sexual strategies of plants (and patrons of Buffalo Bill’s) aren’t necessary, are they?

The short answer is that sex produces offspring that are different, and the variety among individuals is necessary for the long-term success of a species. That way, plants avoid the "hillbilly syndrome" of degeneration caused by lack of cross-fertilization. Plants sometimes resort to self-fertilization (incest) when pollination fails, but generally do their best not to. Their main defence is to off-set the timing of puberty for male and female parts – pollen is produced at a time when the female parts on the same plant are not receptive.

We’ll have more thoughts on the ingenious ways plants attract pollinators in future columns. If you can’t wait, ask Joan and Suzanne for your own inter-library loan of The Sex Life of Plants . They’ll never look at you the same way again.

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Sightings and Memberships: NatureSpeak is prepared by the Whistler Naturalists. To become a member or to report noteworthy sightings of mammals, birds, or other species, contact Lee Edwards (905-6448; e-mail: leighe11@hotmail.com).