Caruncle - Seed Appendages
This is a white, collar-like structure borne on the micropylar end of the seed in many members of the Euphorbiaceae, such as castor, Ricinus communis. The soft outgrowth capping the hard seed is formed by proliferation of the cells at the tip of the outer integument. It is rich in starch and sugars. The violent opening of the fruit (this is termed gun-shot mechanism) causes seeds to be thrown away a few feet. It is believed that ants consume the caruncle and in the process carry the seed further away. The caruncle is also considered to be hygroscopic and it may be helpful in absorbing moisture for seed germination.