10 



ON NAIAS GBAMINEA DEL., VAB. DELILEI MAGNUS. 



VII. — The Leaf-sheath. 



The leaf-sheath is another important character in distinguishing 

 the species of Naiadm, the extent of the dilatation, and the form of 

 the auricle, when present, furnishing useful marks of discrimination. 



The types given by 

 .Braun in the 'Journal 

 of Botany,' vol. ii., p. 

 274, are re-drawn on 

 Plate 251. figs. 10 to 14, 

 but, as will be seen from 

 what follows, the Bed- 

 dish plant differs con- 

 siderably from Braun' s 

 figure of N. graminea, 

 unless he meant it to 

 serve as a general figure 

 of the type of sheath 

 in his super-species N. 

 tenvivfolia. 



In the English Nairn 

 graminea the base of the 

 lamina of the outermost 

 pair of leaves suddenly 

 dilates into a pair of 

 upright auricles, or ears, 

 which are continued be- 

 low so as to form a more 

 or less ample sheath (see 

 fig. 52) ; the size of the 

 sheath presents con- 

 siderable variations, ac- 

 cording to the age and 

 the position of the leaf 

 to which it belongs (see 

 figs. 52 to 55). I see no 

 trace of any intravaginal 

 scales (squamulse) at the 

 base of the leaf-sheath, 

 such as are found in 

 s^*^ Naias major and in the al- 

 f y^^ lied genus Phucagrostis. 

 If Fig.29,Plate 251, shows 



I the scales of Naias major 



in situ ; one of the scales 

 is drawn separately in 

 fig. 30 on the same 

 plate. 



The auricles in their 

 turn vary in shape and 

 size, but I have not met 



Fig. 53. 



