Pollen transfers through air currents (as anyone with allergies I bet has dealt with). Tomato plants are often pollinated by gently shaking the plant stalks. That shakes the pollen fall from the flowers, and thus travels to the others flowers through air currents. You can also use a oscillating fan to circulate air currents. Or there's always the old fashioned way, have sex with them yourself (hand pollinate).

for tomatoes, buy a cheap electric toothbrush and just vibrate the back of the flowers for a second or two. it'll only take you a few minutes and, when I've done it several times over a week I had 100% fruiting.

Oh Goodness, Grizzman

I got a good laugh out of that, picturing oneself out there with a vibrating toothbrush! I'm sure it is effective, but I can't help but wonder if your 100% fruiting record is not only because of the pollen, but because your tomatoes were SO HAPPY with your attentions!

*grin*,
Jane

If you plan to use a toothbrush, vibrate the opposite side of the stem just below the flowers for a couple of seconds. That way you won't beat up your flowers. It works best if your temp and humidity are in the "comfortable zone" for people. Otherwise, the pollen doesn't release or stick properly and you get malformed tomatoes.

If you're growing tomatoes, you can use the same nutrient solution for european cucumbers. You can buy gynoecious seeds (all female flowers) that do not require any outside pollination. If you go this route, remember that cucumber plants need twice as much space and twice as much nutrient solution as a tomato plant.