OP NAIAS GRAMINEA, VAR. DELILEI. 35 



aggregated ; surrounding these is a layer of much larger 

 cells_, hexagonal in outline^ and having thinner walls than 

 those which protect the central channel. From this cen- 

 tral mass radiates a series of from eight to twelve prolon- 

 gations of the central hexagonal cells^ meeting as many 

 outgrowths from the tissue which forms the circumference 

 of the internode, and arranged like the spokes of a wheel. 

 See fig. 42. 



The rays enclose an equal number of large intercellular 

 cavities^ each cavity being bounded by the central and 

 peripheral parenchyma 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 intercellular 

 cavity. 



The circumferential tissue of each internode consists of 

 three or four rows of elongate cells having a hexagonal 

 outline, with 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 difiers 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 

 Eeddish plant. I reproduce Parlatore's figure on Plate VII, 

 fig. 36. 



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