Wilderness Underfoot: What seeds really want

StoryImage( ‘/Images/Story//Auto-img-11097803454811.jpg’, ”, ‘Dandelions – Although they agressively send out seeds, they also rely on tap-roots to reproduce.’);
StoryImage( ‘/Images/Story//Auto-img-11097803842163.jpg’, ”, ‘Acorns (the seeds of oaks) – Some must be planted soon after they fall to the ground, while others must winter-over first.’);

Seeds have evolved the ability to germinate at just the right time…

Now is the part of winter when gardeners get the itch to pore over seed catalogs and stroll the aisles of nurseries. Spring is coming with its promise of rainy days, warming weather and new growth. This is an excellent time to muse over the seemingly magical properties of seeds.

The sprouting or “germination” of seeds is more complicated than one might think. It is not as simple as burying them under soil and adding water – although many of the domesticated garden seeds we use today have been selected to do just that.

In the wild, seeds need protection from germinating at the wrong time, such as during droughts, before hard frosts and winter weather, or when conditions make survival of young plants unlikely. To gain the best chance of success, seeds have evolved special triggering mechanisms.

The most common germination trigger in seeds here in the north is referred to as “stratification” – a period of cold, damp burial, which is then followed by a warming trend. Essentially, this means these seeds must first winter-over. In the spring, some seeds must then be exposed to light, while others need darkness to germinate. Stratification helps plants avoid sprouting just before freezing weather.

Seeds aren’t always the primary method of plant reproduction; often they are the backup strategy. Many plants spread through new shoots that emerge from their deep taproots, tubers or long horizontal roots. Others rely on horizontal stems known as “runners,” or branches that arch down to the soil and take root as new plants. Some plants have branches that can take root even if they fall free from the parent. Where nature is lush and thriving, seeds may wait to germinate until after disaster strikes and the primary reproductive strategies fail. This ensures the ability of a habitat to replant itself.

In fact, some seeds seem unwilling to grow at all unless the surrounding habitat is struck by a catastrophe – a ravaging fire or flood, for example. One study revealed that seeds of certain plants growing on the edges of rivers and ponds seem to favor disastrous floods. These seeds can wait deep under the ground for years until a flood rips away the upper layers of soil and vegetation. Exposure to sunlight signals that an opportunity has come to germinate and gain a foothold in the newly stripped topsoil.

Perhaps the most unusual adaptation of seeds involves herbivorous animals. Plant-eating mammals and birds had a great influence on the evolution of plants. Some seeds developed hard shells to survive being crushed under hooves, or ground by teeth and passing through an animal’s digestive system. Many of these seeds now require “scarification”– scratching or scarring of the seed coat – before they will sprout. A large percentage of the hard-shelled seeds passing through these animals come out perfectly viable and ready to grow!

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