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Part 5: Plant reproduction

4. Stimuli that break dormancy

The seeds from different species of plant are brought out of dormancy by different stimuli. Most seed respond to more than one stimuli, so mimicking one condition when breaking seed dormancy may not be enough.

Some seeds germinate once they have dried out to a certain extent. For the majority of seeds if they dry out so that they contain less than 5% water they can be damaged. Pine trees are included in this group

Swiss pine trees in the foreground with mountains behind and blue skies.

Swiss pine trees (pinus cembra)
Wolfgang Moroder / CC BY-SA 3.0

Some seeds require extreme high temperatures for the seed coat to be broken to allow germination to take place.

Red - orange - tubular shaped flowers on a single stem in an otherwise barrent, sandy terrain.

The fire lily (Cyrtanthus ventricosus)
Callan Cohen / CC BY-SA 3.0

Some seeds will not germinate unless they have been eaten and excreted.

A waxwing sitting among snow covered branches with a bright red seed in its mouth.

Bohemian Waxwing eating a berry, Kenai National Wildlife Refuge, Alaska
Lisa Hupp/USFWS / Public domain

Some seeds need a cold treatment to germinate which mimics the seeds going through winter. Once the cold spell is over,they germinate in the spring. The process of chilling seeds is often referred to as stratification.

A clump of purple blooms on leafy green stems growing in shingle on the side of a mountain.

Penstemon eriantherus var. whitedii requires stratification
Thayne Tuason/  CC BY-SA 4.0