ANATOMY OF LEAVES OF SUBMERGED AND EMERGENT FORMS OF LITTORELLA-UNIFLORA (L) ASCHERSON

Littorella uniflora (L.) Ascherson is able to grow successfully both under submerged and emergent conditions. After emergence, the submerged leaves die within a short time and aerial leaves are formed within a few days. The general architecture of both leaf forms is the same. The epidermis is thin and does not contain chloroplasts. The mesophyll is disintegrated into many lacunae; the cells are large and have large vacuoles. Chloroplasts are of the granal type with plastoglobuli and starch granules. The leaf has three vascular bundles, one large bundle and two smaller ones located in the upper mesophyll tissue, forming a kind of triangle with the central bundle. The xylem is well developed and shows spiral tracheids. As a consequence of greater lacunar space, the diameter of the submerged leaf is about two or three times larger, as compared with the aeriel leaf. The submerged leaf seems to be distended. The epidermis of the submerged leaves lacks stomata, whereas aerial leaves show many stomata of the Helleborus type. In submerged leaves, the central vascular bundle is in direct contact with the surrounding water. The same observation was made in aerial leaves after submersion, whereas in normal aerial leaves the central bundle is closed.