ON NAIAS GBAMINEA DEL., VAB. DELILEI MAGNUS. 7 



The rays enclose an equal number of large intercellular cavities, 

 each cavity being bounded by the central and peripheral paren- 

 chyma at either end. The cavities occur in every internode, 

 whatever its age, but they are limited in the direction of the axis 

 by the node. The rays consist of a single row of cells, except at 

 the points where they join the circumference and centre ; they are 

 not always as regular as they are drawn in fig. 42, as they 

 occasionally branch at each end so as to enclose a smaller inter- 

 cellular cavity. 



The circumferential tissue of each internode consists of three 

 or four rows of elongate cells having a hexagonal outline, faith 

 sinuous edges. The cells are all uniform in size, the outermost 

 layer not being smaller than the rest, as it is in Naias flexilis. The 

 external edge of the outer row of cells is slightly thickened, but I 

 cannot detect any epidermal cells. 



In the posthumous work of Prof. Parlatore, entitled ' Tavole 

 per una "Anatomia delle piante aquatiche,"' a drawing is given of 

 the transverse section of the Italian Naias graminea, but it differs 

 from my drawing (fig. 42) in showing an epidermis of distinct 

 square-shaped cells. The central bundle is also made to consist of 

 about half a dozen rows of cells, smaller in size than I find them in 

 the Beddish plant. I reproduce Parlatore's figure on Plate 252, 

 fig. 36. 



Chatin, in his valuable but incomplete work, ' Anatomie com- 

 pared des Vegetaux,' did not quite reach the Naiadaaea in the 

 volume devoted to aquatic plants, or his drawings would have been 

 useful for comparison ; it is much to be desired that this fine work 

 had been completed, as well for the parasitic plants as for the 

 aquatic. The Naiada, are not yet figured by Eeichenbach in his 

 ' Icones Florae Germanicse et Helvetic*,' &c. 



V. — The Leaves. 



)v, The leaves grow in tufts at the side of each inter- 



node, and they are rather more lateral than they are 

 represented in Delile's figure, reproduced two-thirds the 

 original size in Plate 250, fig. 3. In the living state, 

 as seen in the water from above, they have a light 

 olive-green shade, much duller than that of the bright 

 green leaves of Naias flexilis. In the dried state they 

 become much darker, particularly in the older leaves, 

 but the younger tufts retain the light green colour of 

 the living plant. 



In shape the leaves are linear, broadly channelled 

 in their lower portion (figs. 64 & 65), thickened in the 

 region of the midrib' (figs. 60 to 63), and slightly 

 keeled on their lower surface ; in length they vary 

 from i in, to If in., and they are l-24th in. broad 

 or less (see Plate 249, fig. 2). The sides of the fully- 

 developed leaf are parallel for the greater portion of 

 their length, but at their base they widen out into a 

 Fig. 43. broad sheath bearing two upright auricles applied to 



