22 



ON NAIAS GKAMINEA DEL., VAR. DELILEI MAGNUS. 



and in the middle fruit of figure 86. This division of the beak into 

 i , two branches is a constant character, and very clearly distinguishes 

 •4f* it from the four-rayed beak of Naias ftexilis (fig. 87). 



5N !lfi 



Fig. 86. 



Fia. 87. 



One other point of differentiation between Naias graminea and 

 N.flexilis rests in the shape of the fruit. In the former the ends 

 are more abruptly narrowed into the base and the beak than they 

 are in the latter, which has gradually narrowing ends ; compare 

 figs. 86 and 87. Cesati's figures in 'Linnsea' xxxii., Plate 2, 

 confirm this conclusion. 



The perianth easily separates from the fruit ; it 

 is represented in fig. 88. The portion which covers 

 the body of the fruit consists of a single layer of cells. 



XV.— The Roots. 



The roots are of great length, creeping in the soft 

 black mud of the bed of the canal ; they are given 

 off from the nodes in verticils. They are capillary, 

 uniform in diameter, even when nine inches long, 

 tawny-orange in colour, and I have not seem them 

 branch. 



In internal structure they bear some resemblance 

 to the stems. There is a central channel surrounded 

 by a mass of elongate cells hexagonal in outline, 

 smaller in size, and with thinner walls than those of 

 the rest of the cells within the cylinder. Outside this area is 

 a row of cells whose walls are darker coloured than any of the 

 others (except the cells which form the exterior of the cylinder), 

 and they so arrange themselves as to form a sheath round the 

 central cells ; from this row of cells numerous short branches are 

 given off whieh enclose intra-cellular cavities, similar to those 



Fia. 88. 



