Hypostase is one of the unusual features present at the chalazal region of the embryo sac and situated immediately below it. It represents an irregularly outlined group of nucellar cells which are poor in cytoplasmic contents but have their walls partially lignified or suberized.
The name Hypostase to this group of unusual cells was first given by Van Tieghem. According to him the hypostase forms a barrier or boundary to prevent the further growth of the embryo sac.
Even though hypostase is limited to basal region of the embryo sac occasionally they may cover the embryo sac extending up to the micropylar half.
Hypostase has been reported from a number of families Amaryllidaceae, Villiaceae, Zingiberaceae, Euphorbiaceae, Crossomataceae, Theaceae and Umbelliferae.
At the stage of the organized embryo sac the cluster of hypostase cells appear like a beard at the chalazal region of the embryo sac.
|HYPOSTASE OF PLANT (ANATOMICAL VIEW)|
I. It prevents excessive growth of the embryo sac of the chalazal region acting as a barrier.
II. It plays a role in the water balance of the resting seed.
III. It serves as a link between the vasculature of the funicle and the embryo sac facilitating the rapid transport of the nutrients.
IV. It may acts as secondary storage tissue.
V. It produces certain enzymes or hormones and has a role to play in the protection of the seed.