ON NAIAS GKAMINEA DEL., VAB. DELILEI MAGNUS. 



13 



Fig. 61. 



Fig. 62. 



the superior and inferior layers which Dr. Magnus mentions on 

 p. 51 of his ' Beitrage.' No doubt the cells of the convex side ef the 

 lamina are slightly the smaller, but the difference is not so marked 

 as they are represented in Plate 252, figs. 31 to 33, which are 

 copied from the figures given by Dr. Magnus. 



There are no stomata on the leaves, 

 and no epidermis ; but the surface-cells in 

 all parts of the plant have intermixed with 

 them reddish pink pigment-cells, which 

 become brown with age. They are probably 

 resinous, as they are the last to decay; 

 similar cells occur in other species of 

 Naias. 



The central portion of the leaf is 

 much thicker than the sides, because at 

 this point the two layers of the lamina 

 diverge from each other so as to enclose a 

 central bundle of small-sized cells, sur- 

 rounded by a layer of six or eight larger- 

 sized cells. On either side of this central 

 tissue are two intercellular cavities, which 

 greatly exceed in size the cells which bound 

 them (see figs. 60 to 65). 



In his 'Beitrage,' pp. 51 and 52, Mag- 

 nus describes Naias graminea as possessing 

 bast-cells in certain fixed positions in the 

 leaf, namely, close to the margin, and im- 

 mediately above and below the central 

 bundle on the upper and lower surfaces of the leaf (see figs. 31 to 33 

 on Plate 252). These bast-cells I cannot discover, after prolonged 

 search, in any portion of the Eeddish plants ; but as 

 Magnus states (p. 52) that Damietta specimens collected 

 by Ehrenberg, and Cairo specimens collected by 

 Schweinfurth, also have these bast-cells wanting, it is 

 clear that the Eeddish plant corresponds in this par- 

 ticular with the plants from Lower Egypt. 



On the other hand, the plant from the Italian sta- 

 tions possesses bast-cells. I found them clearly marked 

 in specimens in my herbarium collected by Signor 

 Malinverni, " In stagnis fossis et oryzetis circa Quinto 

 Vercellensis ditionis pago sestate 1875"; the accom- 

 panying figure has been drawn from the leaf of one of 

 these plants (fig. 66). 



The line of libriform cells is the central one of the 

 three series which I have drawn ; it is most clearly 

 apparent when viewed as a transparent object, from the 

 circumstance that its cells do not contain chlorophyll, 

 and hence it is visible as a transparent colourless line 

 in the midst of green tissue. 



An isolated bast-cell is given in fig. 34 on Plate 252, 

 and their position in the leaf is shown in figs. 31 to 33 



Fig. 64. 



Fig. 65. 



1 



Fig. 66. 



