The birds and the bees

…and moths and ants, and the occasional bat, and sometimes just a good stiff wind. Sorry to disappoint — this is about plant sex. It’s gardening season, so in honour of the new White House kitchen garden, here’s a refresher on how plants make whoopie.

I’ve never seen plants having sex! In biology jargon, sexual reproduction simply means that two parents combine their genes to make offspring. As mammals, we associate the word with physical arousal, warm snuggly feelings and undignified athletics, but other life forms have different ways of sharing their genetic material.

Where does a plant keep its naughty bits? Most of the plants in your garden are probably flowering plants, and the flower is the reproductive system. Remember that the next time you stick your nose in one.

How do you tell a girl plant from a boy plant? The most useful question to ask is whether a given plant has male parts (that produce pollen, a.k.a. sperm), female parts (ovaries that produce and protect ova), or both. For some plants, each individual has only male flowers or only female flowers. For others, each individual plant has some flowers with male parts and some with female parts. The most common arrangement in your garden is for every plant to have both male and female parts on every flower.

So how do they, uh, “do it”? There’s usually a third party involved. (Oo-er, missus.) An insect or a bird or a bat visits a flower and inadvertently gets pollen stuck to its body, which gets transferred to the next flower visted. Critters visit because the plant offers them food (usually a sugary liquid called nectar, which they can get to without damaging the flower). They know the food is there because of the pretty colours and nice smells that are the flower’s way of advertising its presence. A flower without food to offer to a pollinator, and without a way of letting the pollinators know where it is, would have a slim chance of reproducing. That said, there are ways around this problem. A pine tree’s male flowers are inconspicuous little spikes that don’t rely on animal pollinators — they just let their pollen blow away in the wind to land on the female flowers (also known as cones) of other pine trees. (Think about that the next time you see that powdery yellow pine pollen all over everything!) Some flowers’ pollen can actually fertilize the ova in the same flower, so it doesn’t even need to travel.

I’ve never seen a pregnant plant, either. Actually, you have — if you’ve seen fruit hanging from a tree, you’ve seen a pregnant plant. After the ovum is fertilized by the pollen, the petals of the flower drop off (they’re just advertising, so their work is done). Fruit grows out from the ovary, protecting the developing embryonic plant — i.e. the seed. Fruits can be anything from simple little nuts or pods to big extravagant juicy constructions, all evolved to protect, nourish, and/or transport the seed. The fruit of a maple tree is a papery little pod with a sail-like feature that helps it travel away from the tree when it falls. The fruit of a blueberry bush is a tasty little purple thing that lots of animals like to eat, and with luck the seeds will survive the trip through the animal’s digestive system and end up planted in a nice pile of poo somewhere far from the plant.

If you can think of anything that I’ve missed, leave a comment. I am happy to talk your ear off about plants.  


1 Comment

  1. Pebblerocker said,

    20 March 2009 at 8:38 pm

    There have been plenty of bumblebees doing the job for my pumpkin patch, but I didn’t realise that the female flowers have little fruits on them already without being fertilised. There are a few little abortions among the growing pumpkins and I hadn’t known why they didn’t develop like the rest.

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