Rick Shory

Offering a little something you might not otherwise have


1 Comment

Germinating mimosa seeds

I thought that the main germination inhibition for mimosa (Albizia julibrissin) was the water impervious seed coat. This is an experiment to check that.

I found some mimosa pods that had just fallen from the tree. Their structure was papery valves (the flat sides), with wiry reinforced edges.

20151124_080445_mimosa_pods

Mimosa pods

It was evident their dispersal mechanism is to be blown about till the wiry edges wear out, allowing the valves to peel apart and drop the seeds. This goes along with the idea that the seeds are blocked from germination until their hard coats are breached, either from erosion by gritty soil, or long rotting in humus.

I took out ten seeds.

ten mimosa seeds

Ten mimosa seeds

I put them in water to soak.

ten mimosa seeds soaking

2015-11-24 08:10

About 24 hours later, two of the ten (20%) were imbibed with water.

20 percent imbibed by 2015-11-25 06:46

2015-11-25 06:46

This verified the seed coat was impervious enough to water to prevent absorption.

seeds, imbibed and not

Compare imbibed to not imbibed.

Breaching an impervious seed coat is called “scarification”. There are various ways to do it to bulk seeds; but for individual seeds you can use a file, knife, or sandpaper.

metal file

metal file

Here, I scratched seeds on a file.

scratching a seed on the file

scratched seed

I rubbed till the lighter colored interior showed through.

seed coat filed through

Seed coat filed through

I also nicked some seeds with a utility knife. I avoided the very tip of the seed, in case I might damage the embryo root, though seeds like this often protect their incipient root by embedding it somewhat back in the embryo.

Here is a scarified seed beginning to imbibe. This seed was both scratched and nicked. The flap towards the top is the nick.

seed beginning to imbibe

2015-11-25 09:19

The water absorption is a chain reaction. As the interior swells, it disrupts the seed coat from the inside, and allows still more water to enter.

Here is the same seed fully imbibed.

same seed fully imbibed

2015-11-25 12:05

The water absorption goes quickly after the seed coat is breached. Here, the seed has become fully imbibed after only a few hours. Many of the intact seeds were still dry inside after twenty-four hours soaking, and could have remained so indefinitely.

In order to closely observe the seeds, I put them in a standard germination test setup, rather than planting them in soil.

Here they are along the top of the folded, wet paper towel.

seeds on wet paper towel

I close the fold, and rolled this up on a chopstick.

seeds rolled up in wet paper towel

I held this, in light, at warm room temperature, about 80 degrees F.

seeds rolled in paper towel, standing in jar of water

2015-11-25 12:15

Within 48 hours, I had 100% germination.

ten mimosa seeds germinated

2015-11-27 09:01

close up of germinated seeds

close-up

This demonstrates that mimosa seeds’ germination requirement is primarily imbibation with water, and warm temperature. There is no inhibition by light, and no chilling requirement.

This explains why mimosa seldom volunteers in Portland. The time of year when temperatures are warm enough is also the driest weather. Seedlings that germinated in early summer would fail from drought later.

 


2 Comments >

Botanical term: “Imbibe”. Most seeds can remain dry-dormant for long periods of time. When they take in moisture to capacity, they are said to “imbibe” it, or to “become imbibed”. Some seeds, like the beans used for food, noticeably swell. Others, like tree seeds such as apples and maples, do not look much different. In these cases, the main change is internal texture. The plant embryo, which was hard and brittle when dry, becomes leathery or soft.

The state of “being imbibed” with moisture is distinct from simply “wetted”. Seeds with an impervious coat may not become imbibed, even when soaked in water. On the other hand, many seeds will become fully imbibed when placed in soil that seems scarcely moist to the touch.