THE AUSTRALIAN GREY MANGROVE. 261 



PI. Ind., 1481-2, which has quite a different shaped leaf, 

 stamens, ovary and pistil from those of the Australian 

 plant. It more nearly approaches in its organs the figures 

 of A. alba, which is recorded as a small tree or shrub as 

 against the large sized tree of the Australian Avicennia. 



Linnaeus, himself, later reduced his A. officinalis under 

 A. tomentosa a name now restricted to the American tree, 

 an action which seems rather to have confused matters, 

 and in opposition to this I propose to restore Linnaeus' 

 original name until a correct description is available, as 

 well as an original specimen for comparison. 



In order that the species may be more definitely placed 

 in future, features other than morphological have been 

 investigated, especially the microscopical structure of its 

 several parts or organs, such as leaves, pneumatophores, 

 timber, bark, and germination of the seed. 



5. Leaves. 



These trees as a rule have a most luxuriant growth of 

 leaves, and this is what might be expected in view of the 

 fact that the ash of the wood contains a high percentage 

 of potassium salts (infra). 



(a) Histology. — A transverse section, (Plate XXVII, 

 figure 1) shows the structure of this organ to be quite 

 unique. Except for one row of epidermal cells the upper 

 half is composed entirely of a delicately walled material of 

 irregularly shaped cells, evidently for water-storing — the 

 *' water tissue" as now understood, the larger cells being 

 towards the middle of the leaf. This structure is succeeded 

 in the lower half from the central axis of the blade by three, 

 sometimes four rows of palisade parenchyma, which occupy 

 the slightly larger part of this half of the leaf, and is 

 followed by thin-walled loose parenchyma cells, or spongy 

 mesophyll. Throughout the structure are scattered trachea 



