Seeds – from the grain to the plant
"The seeds of the past are the fruits of the future" – Buddha
A well-known philosophical question says: “What came first, the chicken or the egg?”. The philosophical approach is clear: A chicken can only grow from an egg, but in order for the egg to exist there must be a mother before, meaning a chicken that has laid the egg. If the question is purely evolutionistic, then the question has been answered: The Egg is the response. If this is to be transmitted to the plants, then the answer is not that easy. If the question would be – What came first – the seed or the plant, then in this case the answer would be: The plant.
Why it this so? Simple: Not all the plants are multiplied trough seeds. Moss can multiply trough cell division. This cannot be only done by moss, but also by a series of “higher” plants that can reproduce vegetative, meaning that they produce offsets. Some plants can also do both – strawberries are such an example. The plants that have seeds in order to reproduce build up a big group. The majority of the vegetables and fruit are part of it – even if there are other natural ways of multiplying these plants.
Spreading through the air
The propagation of the plant through the use of seeds is quite comfortable – especially if there are animals and people in that area. In the process the ripe fruit of the plant are ingested and the seeds are then expelled with a great portion of fertilizer and all this in another spot. A very good example are the chilies and the wild birds. The small red fruit of the wild chilies like Chiltepin, Ulupicas or Cumari are the food of birds. The vast majority of birds do not have receptors that react to the heat of the capsaicin. For these the chilies only taste fruity and in the best case also sweet. Because the vast majority of wild chilies are small and they grow upwards these can be picked up very easily by the birds and are an easy snack. Dive in, open the beak, swallow the chili and away they go. Because the birds have a fast digestion the seed does not need to stay for a long time in the stomach. The time that the seed spends in the stomach is ideal, because the shell of the seed can become soft trough the acids in the stomach. The plant fertilizers that are contained in the bird droppings make for a perfect stat for the seed. Because the birds travel far and fast there is nothing standing in the way of the plants rapid expansion. If the conditions in the soil are fitting where the bird has left the seeds then a new plant can grow there.
The same scenario is applicable for the majority of plants that have seeds: depending in the region from where they come from there are different ways of transportation for the seeds, but the animal transportation is very common.
Plants have group Sex
Even if this sounds like a catchy title this is in praxis exactly like that. In a lot of cases the blossoms are made out of two parts – a masculine and a feminine part. Think about the bee and the blossom. In this case the bee does not have such an important role. A large part of the vegetables is able to reproduce alone. Just alone will not do, but a little bit of wind that shakes the blossom will do. Rhythmic motions like for humans will also do. It is not important if the pollen from one flower mixes with that from another, but in order for one flower to pollinize the other it has to go a longer way. In order to aid that they use the wind and other insects like the bees. This is why we can say that the plants have group sex.
From the fruit to the seed
When a flower is polemized, if the conditions permit it a fruit will grow from it. And in this or attached to this fruit the seeds will grow. These are practically an embryo that is contained inside a sleeve, which can be compared with an egg. In the seed, besides the reproductive tissue there is also moisture and fertilizer. Practically, there is everything that a plant needs in the first hours in order to survive. The seed is covered by a seed coat. This seed coat is essential, because the seed would have been digested when the birds would eat it. The seed coat offers also protection in case of exterior threats. The seed coat is made specially to assure that the seed can germinate: depending on the necessities, the seed coat is different and also has a different form. The gemination is determined by two parameters: moisture that can enter the seed and minimal temperature that the plant needs in order to develop.
Therefore, it is also interesting to know how the interior of a seed looks like. The following picture shows a longitudinal cut of a Capsicum Pubescens chilli seed. It can be clearly observed that beneath the black seed coat there is a natural layer that functions similar to the egg white. In there is the material that will germinate.
Different colors, sizes and forms
Still it has not been clarified what influence the color of a seed has on the further development and also on the spreading of the variety. There are some theories but there is still a lot of room for further studies. One of the theories is that the color helps protect the seeds against predators. This way a seed that has the same color as the substrate can be found more difficult. This makes sense especially for bigger seeds with a thicker skin: A thicker skin means that the seeds are protected against the exterior elements and that the germination period is also longer. For some varieties that have a really thick outer shell it can be that the germination takes place only in the next year or maybe after more years – when the seed is pushed through the exterior elements into the soil. Another mechanism that is used for germination can be seen more in the small seeds and the fast germinators: they need, in order to germinate light, which points out to a fast multiplying cycle.
Also, the form is decisive: the more loose and lighter the substrate is in which the plant grows, the harder it is for a seed that has a smooth shell to dispose of it. A wrinkled form can also have another reason behind it: when the roots of the plant have to dig deep in the earth before it climbs to the surface the texture acts like a barb and helps the roots dig further in the earth.
How different the actual surface of the seeds is can be seen in the CT image that the company Strube GmbH & Co. KG has kindly made for us.
The images show two 3D pictures of a Rocoto CAP357 (capsicum pubescens) and a Jalapeno (capsicum annuum) that show how smooth the Jalapeno is when compared to the Rocoto – and which indicates how the roots grow and what the preferred growing place of the seeds is.
Important for the plants is (almost) only the moisture and the temperature
Besides the conditions like light or darkness (for a lot of seeds this is not important since they germinate as well in the light as in the dark), there are no conditions that a seed needs in order to germinate, besides the correct temperature (This is the way that the seed “knows” that the vegetation period begins) and enough moisture.
A ”soaking” in water, in chamomile tea or 1% saltpeter solution has been researched in small trials and is now part of an ongoing study. The results show that there are only minimal changes visible. If the substrate is moist enough (and has the right nutrients), then the soaking parameters are already met: for the seed it is not important if it has soaked for a day or if it is put directly in the moist ground and gets the moisture from the earth. Saltpeter solution is present in a small amount also in the earth. It does not occur directly, but in the form of the both plant nutrients potassium and nitrogen that are tied to other elements that are available for the plant. If you don’t leave the seed to germinate in a germination box, in which it could play a role if there are nutrients present or not, it seems that also the saltpeter solution is obsolete. Conclusion: a soaking does bring small advantages, but most of the time it is not necessary.
More decisive is the germination temperature: while tomatoes are undemanding, the chilies are a little bit pickier. Tomatoes can germinate – even if it takes a little bit longer and it is harder from a temperature above 15 degrees. 24 to 27 degrees are optimal for the tomatoes. The chilies like it a little bit warmer: 20 degrees should be at a minimum, optimal are 27 up to 30 degrees.
Text by Nico Jäkel