Testa of seed consists of four layers which becomes hard and woody after ripening. The presence of aril outside the testa may increase the buoyancy of the fruit. 芡种子的种皮共有四层,成熟后坚硬,种皮外有假种皮,有增加浮力的作用。
aril
[ noun ] fleshy and usually brightly colored cover of some seeds that develops from the ovule stalk and partially or entirely envelopes the seed <noun.plant>
Aril \Ar"il\, ||Arillus \A*ril"lus\, n. [From LL. arilli dry grapes, perh. fr. L. aridus dry: cf. F,. arille.] (Bot.) A exterior covering, forming a false coat or appendage to a seed, as the loose, transparent bag inclosing the seed of the white water lily. The mace of the nutmeg is also an aril. --Gray.