Appendix 2: Pretreatment of hard–seeded species

Pretreatment of hard–seeded species

Seeds of these species possess a thick, impermeable seed coat which prevents germination by significantly retarding water uptake, respiratory gas exchange or both. Pretreatment consists of removing, splitting, puncturing (Figure A2.1), abrading (Figure A2.2), softening (Figure A2.3) or burning (Figure A2.4) the hard seed coat – without damaging the embryo within.

The following species are the only seeds of woody plants which do not need to be moist in order to respond to any pretreatments, but they need subsequent moistening to germinate.

• broom (Cytisus scoparius) • common laburnum (Laburnum anagyroides) • false acacia (Robinia pseudoacacia) • gorse (Ulex europeaus) • Scotch laburnum (Laburnum alpinum) • tree lupin (Lupinus arboreus)

Figure A2.1 Chipping Hold seed down with an eraser. Use a sharp knife or scalpel to chip away a small section of seed coat without significantly damaging the embryo. Wear safety spectacles. Figure A2.3 Softening

Pour 3–10 volumes of boiling/hot water on to 1 volume of seeds. Allow seeds and water to cool for 18–24 hours. This will give time to observe whether the majority of seeds have swollen through imbibition or not.

Figure A2.2 Abrasion

Use a file or abrasive paper to remove a small section of the seed coat. Figure A2.4 Burning

Make a small hole in the seed coat with a soldering iron or a hot instrument from a fire.