Friday’s seeds – soak, cut & nick
A timely post; these methods may come in handy for all those sowing or preparing to sow at this time of year.
They are not mandatory, one can just sow and be patient; any viable seeds will germinate when the time is right for them.
The purpose of these methods can vary: to check on the status of seeds/embryo, soften the seed/fruit teguments, improve and/or speed up the germination. They can be used for medium to large size seeds but not practical for small and tiny seeds.
Let’s remember first that in order to survive in a dry state over extended periods of unfavorable conditions, all seeds are equipped with +/- impermeable seed coats. Without going into a review of seeds dormancy types, in all cases, the first thing necessary for the ‘awakening’ process, is water absorption/imbibition.
Some seeds can absorb water fast when available, and if also the temperature is optimal, they germinate rapidly; in other cases, this process can take longer, up to many years in fact.
SOAKING
Soaking the seeds in water over various periods of time mimics the natural conditions they would encounter in the fall or spring when the soil moisture is abundant. It is recommended to daily change the water.
Soaking can be done for various purposes: just to hydrate the seeds/fruit teguments or for further exploration; also, it is much easier to proceed with the cutting or nicking after seed coats are soften a bit.
To speed up the water imbibition and thus the processes that initiate the germination.
Also, soaking the seeds for a couple of days will allow for a better absorption of GA3.
As recently shown, in case of Ephedra distachya, simply soaking the seeds triggered their germination (thin seed coats, warm germinator).
For seeds with impermeable coats, just soaking won’t suffice, of course and it needs to be combined with other treatments, like nicking or scarification for example (about scarification next time).
Ruscus colchicus seeds: slighly scarified and soaked for few days; dry seeds to the right. Notice that the seeds have enlarged 2-3 times in size in a very short period of time
CUTTING (SECTIONS)
This is an exploratory method done to visually inspect the status of the insides of seeds/fruits. It allows a quick assessment of the viability/status of the embryo.
The cutting can be done transversal or longitudinal, it depends on the purpose and type of seed/fruit. In all cases it should reveal a whitish/yellowish inside, usually the endosperm in which the embryo is embedded, like shown in the pictures below (in case of immature embryos, they cannot be observed unless using a microscope).
In the case of exalbuminate seeds (no endosperm), the cut will just go through the embryo itself.
Lindera benzoin, sectioned seed
For Caulophyllum species it is an useful method to monitor the embryo development (on seeds kept in moist storage!).
Notice the growth of the embryo over time, in the second year it resemble a small grub :)
In some cases the cut through fruits/seeds can reveal that they are sterile/empty. For species known to have pollination/fertilization problems it is always good to test a small batch of seeds/fruits. Acer triflorum and Franklinia alatamaha case studies are shown below.
Cutting also allows a quick inspection of the thickness of seed coats/fruit wall and provides hints for further treatments. See the case of Triosteum aurantiacum, where the very thick fruit tegument suggests further action in order to allow the water imbibition (scarification).
The very thick/hard fruit wall explains why the seeds would need few years to germinate in natural conditions; by scarifiying as much as possible the fruit wall to allow water penetration to the seed, will speed up the germination
A special method of cutting the seeds can be used to speed up germination for aril Irises. It involves cutting a thin piece from the micropilar end of the seed.
The method is explained in detail HERE. I am currently trying it on a small batch of Iris suaveolens BDob.17 (offered in 2917) and the results are promising!
Iris suaveolens BDob17 – germination start 1 week after the seeds cut (as described in the method above)
NICKING
It involves nicking or chipping of a small area of the seed coat. It is easily done on large seeds with impermeable seed coats.
However, impermeable doesn’t necessarily means thick, and nicking always needs to be done with care.
You would be surprised for example how thin is the seed coat of lotus seeds (Nelumbo species)!
And remember, these are seeds that can maintain their viability for thousands of years!
If a small part of the endosperm/cotyledons is nicked accidentally, it is usually OK.
To be continued…’tis the sowing season!
Really loved this! So interesting and of course educational, the photos are great.
Thank you!
Good tutorial on all things seeds prepration. I adore that first photo!
Thank you Tina. Yes, it always feels good to see seeds germinating :)
For Acer triflorum (and also A. griseum and A. mandshuricum): stand alone trees usually have empty or aborted seeds. When more trees (3 to 5) are in close priximity of each other AND flower at the same time you can get a decent amount of fertile seed (usually still low). Note also that Acer species can hybridise with one another.
Franklinia alatamaha: to my understanding Franklinia needs cross-pollination to get fertile seeds (but I’m glad to be corrected on this one).
True about this, and we can add Acer pseudosieboldianum (probably other species). They all require cross pollination; unfortunately through parthenocarpy they still produce a lot of fruits, deceivingly empty though.
I only had few seeds of Franklinia to look at; the problem may be more complex here because of its unusual fruit/seed forming (reproductive phenology). There is literature available to read about it.