ANATOMY OF ENHALUS ACOROIDES. 359 
THe Lear, 
Accounts of the leaf have been given by Griffiths, Chatin, Magnus, and Sauvageau. 
Griffiths described correctly the coarser features of the anatomy (Chatin gives a descrip- 
tion of the leaves of a plant under the name of Enhalus, but his figures do not accord 
with the structure of the leaf of Enhalus); Magnus added further details, especially 
sbowing the diminution in the number of vascular bundles towards the apex. The 
most complete account is given by Sauvageau, and is summarized as follows :— The 
leaves are long and ribbon-shaped, with a sheathing base, the sheath dwindling to a 
mere line on the side away from the insertion, and are traversed by parallel veins. 
The whole is surrounded by an epidermis, but the internal structure varies at different 
heights. In the middle portion the mesophyll consists only of one subepidermal layer 
of parenchyma on the dorsal and ventral sides. Between these there are numerous 
rectangular air-chambers composed of long lacunze separated by sheet-like trabecule of 
parenchyma one cell thick, at right angles to the dorsal and ventral surfaces, and 
running the longitudinal length of the leaf. 
At regular intervals the lacune are spanned by transverse diaphragms composed of 
one layer of much smaller parenchyma-cells, and separated at the angles by small 
intercellular spaces. Pigment-cells occur in the subepidermal tissue and trabeculw. 
Parallel vascular bundles run the longitudinal length of the leaf. In position they 
correspond to the trabecule, one bundle running in the tissue at the abaxial or adaxial 
region of the trabecula (Pl. 36. fig. 14). "The longitudinal bundles are hence in two 
series in the adaxial and abaxial subepidermal tissues respectively. In most cases 
the two series run in alternate trabecule, but occasionally in the same one. In both 
systems, however, the phloem lies on the side towards the epidermis and the xylem on 
the side towards the centre of the leaf. The abaxial longitudinal veins are connected 
by transverse bundles which run parallel to the epidermis in the diaphragms, which here 
become more than one cell thick. The longitudinal bundles are not all the same size, 
the midrib and marginal ones being markedly larger. Near the apex their number 
decreases. : 
Near the base of the leaf the abaxial subepidermal tissue is from five to six layers thick, 
and the trabeculee and air-chambers are limited to the adaxial side of the leaf. There is 
the abaxial system. Sauvageau explains 
rds:—* Elle provient .... de ce 
au lieu de réunir deux nervures 
dermique de la face 
devenir des nervures 
also only one system of vaseular bundles here, 
the nature of the adaxial system in the following wo 
que certaines des nervures transversales d'anastouose, : 
normalement orientées, se sont dirigées vers la couche Tomo 
Opposée, puis se sont relevées suivant la longeur de la feuille pour 
parallèles aux premieres." 
x this description the following amplificati 
he base of the leaf the intercellular space sys ; 20 
encroachment of abaxial parenchyma (Pl. 36. fig. 4, ©); (2) re a eurn 
cation of the adaxial parenchyma (fig. 4 ©); (3) by the poena her 
cells, so that the trabecule become a mass instead of layer of T = id sarii pe 
(4) by the adjacent trabeculæ becoming connected by rows of cells arrange 
the leaf-surface and at right angles to the trabeculæ (fig. 4, ©). 
ons and corrections may be made :—At 
tem is gradually obliterated by: (1) the 
