|© Melissa Guillet|
It's fall and that means the garden is winding down. Plants prepare for the cooler weather. Flowers, fruits, and pods release their seeds. Fall fruits are entering their harvest time. It's a great time to teach about seed dispersal, or how seeds "migrate".
There are five major ways seeds travel. One of the funnest ones to observe is dispersal by wind. Dandelions did this all summer and a dandelion gone to seed to spread its vitamin C-rich leaves and edible flowers is 15 Minute Field Trips' new symbol, sending environmental literacy and leadership into the world. Now we can see milkweed pods split open to release flat brown seeds carried on fluffy strands. The milkweed plant is critical to the survival of Monarch butterflies as it is the host plant for their eggs and larva. (More about milkweed the plant here and its commercial uses here.) Thistle also uses these silken hairs at this time. Another method using wind includes the samara, or a seed with wing- or propeller-shaped papery tissues such as found on ash, elm, and maple. The flat extension helps the seed journey further from the parent plant on the wind.
Another method plants use is travel by animals. This takes diverse forms. Acorns, for instance, are buried by squirrels for winter storage (where rains will eventually dilute the tannins that make them so bitter), and those that are forgotten or never collected begin their oaken lives. Mistletoe, which as an epiphyte, needs a tree to grow on. It developed a sticky coating on its seeds within the fruits that survives digestion so birds would be forced to rub their tail end on a branch to be free of the seed. Many berries get dispersed by animals through digestion, the seeds left behind in their droppings. Even ants carry seeds off, some of which will germinate underground. Other seeds, such as beggars ticks and burdock stick to animal fur and pant legs with their pointy hooks and spines.
A third method not likely to be seen in a school- or backyard is flotation, as it's seen in aquatic plants. Coconuts, the largest seed, float to new shores, where the tides plant them. Cattails and lotus also use this method.
|Devil's Trumpet found on flickr.com|
An exciting method if you're luck enough to witness it is bursting or popping. Seed pods such as peas, sweet peas, and lupines do this. Devil's trumpet, angel trumpet, and jimson weed, of which we found many in the city compost, is a spiny pod that bursts to release small, black flat seeds. A milkweed pod also bursts first before releasing wind-blown seeds. Catalpa pods are fun to collect and if they haven't split, they make a great rattle. Chestnuts are another burster.
Finally, some plants are dependent of humans to plant them. While I often get squash and tomatoes growing from my compost, corn, beans, and many fruits have evolved through human selection and agriculture.
Fun images of seedpods: Pinterest
If you would like to learn about how to clean and save seeds, the RI Wild Plant Society is having a workshop September 20th, 10-2. Register here.
For a fun seed-sprouting activity for kids using socks, go here.
Also check out the Seed Mobility page on this website!