Most of us at some point have acquired some seeds, thrown them in a little soil and up they’ve come. A little spec of dust starts as a couple of leaves poking out of the ground and over time becomes a great plant, leaves, flowers and everything else you’d expect. Maybe you have or maybe you haven’t ever thought about what actually happened? How did that tiny seed start to form into something else, it’s either magic (which I suspect is involved), or there is a logical chain of events that kick in when the conditions are right and the germination process is triggered?
In many cases it’s not just about the conditions, some seeds require a special set of circumstances before they’ll even start to think about germinating, even if the conditions are ideal. For me, this is the most fascinating part of the process of growing plants and something that’s important to know if you’re going to be more successful than not.
Seeds are said to be dormant until the point that they start to germinate and to break that dormancy sometimes you need to chill, heat, or even break the casing a little called scarification. Environmental variables like fires or severe cold can be required for some seeds to break dormancy in their natural locations, these conditions are usually fairly easily replicated by us, though.
Some seeds are so small that there is little stored energy for them to grow much before they start to need access to the sunlight and some energy. These will sometimes require light as a trigger for them to germinate as this signals to the seed that it’s on or near the surface and won’t have far to go to get to the surface. Without that trigger, if they tried to germinate when they were an inch below the soil they would have run out of energy before they even saw the light of day. Luckily for us, most seeds that we sow need none of this and will just grow with a little warmth, some moisture and a bit of patience.
Most seeds that we grow are divided up into two groups of angiosperms, monocot, and dicot, this refers to the number of cotyledons that the seed contains. This is most obvious when you see the seedling appear as dicots have two seed leaves like a bean and a monocot will have one, such as sweetcorn and grasses. The difference was identified as early as C 370 BC but we still identified plants only by their growth form until the 1600s.
A cotyledon is part of the embryo in the seed that often becomes the seed leaves that you see emerging from the soil, they contain food reserves that the plant needs to get started and in the case of epigeal germinating plants are photosynthetic so they act as normal leaves do too. In hypogeal germinating plants, the cotyledons remain under the ground and send up the hypocotyl with the first leaves at the top, as in the case of a runner bean, whereas epigeal germinating plants send the cotyledons up on the hypocotyl to form the first leaves. Again, this is easy to spot as the first leaves that come out of the soil will often have the seed casing still attached that gets shed soon after the leaves swell.
The first part of the visible germination process, however, is the seed sending down the radicle, the embryonic root that appears from the micropyle in the seed. This will often be covered in what are root hairs, these increase the surface area and allow the plant to take up all the water and nutrients that it will need, at this point though the plant is still running off the stored energy that was in the seed to start with.
|Hypogeal (bottom left), epigeal (top left) and monocot (top right). This is not my image so I’ll swap it out for a better one soon.|
next is a bit about the parts of the seed that’ll hopefully explain better how it all starts and how this process occurs. Germination II