Front Range Seed Analysts
1997 Seed Forum Volume 11 Number 3
SEED NOTES: Ceratonia siliqua L
By Annette Miller
Ceratonia siliqua L., the chocolate substitute carob, is in the Fabaceae family. It is well described and illustrated in USDA Agriculture Handbook 450 by the Forest Service (the big green tree book). I recently had the opportunity to germinate some of these lustrous brown seeds and tried a number of different treatments.
Hoping to avoid the use of sulfuric acid, I attempted seed coat clipping, partial seed coat removal, complete seed coat removal, cotyledon clipping, and short prechills followed by germination (or more accurately death) on top of blotters in boxes at 20 C. The embryos stained well in TZ and showed no evidence of decay or insect damage. Finally, donning acid proof gloves, goggles and a rubber apron, I soaked the seeds in concentrated sulfuric acid in a small glass vial (placed under a fume hood) for the prescribed one hour. Using a strainer, I rinsed the seeds in a bucket of water for 20 minutes. Then I placed them on germination towels at 20 C. All the seeds germinated beautifully with no mold or other discernable damage from the acid treatment.
Though the acid appears black after use, acid it can be reused. However, since we used such a small quantity and we use it so infrequently, the acid was diluted with water and neutralized with NaOH before disposal down the drain.
The ecology of seeds that respond to acid scarification is usually explained by a symbiotic relationship of the plant to an animal that ingests the fruit and passes the seeds through its gut, thus scarifying them with acids from the digestive tract.
For Ceratonia, (and many other species) we know that it works but we don't know why. Why would acid scarification work where excision fails? Is light inhibitory? What is in the remaining rubbery endosperm that is such a strong germination promoter? After treatment, does the endosperm then become a sink for germination inhibitors located throughout the embryo? This latter hypothesis appeals to me most. However, I leave further investigation to others with a more thorough background in physiology and biochemistry.