ON NAIAS GRAMINEA DEL., VAK. DELILEI MAGNUS. 



the stem and half-clasping it (figs. 52 to 55). The 

 extremity of the leaf is gradually attenuated, and ends 

 in from one to three spines (fig. 43) ; the extremities 

 are frequently truncate, so that the spines give it a 

 cuspidate character (fig. 44). 



The margins of the sides, sheath, and free ex- 

 tremity are studded with erect, unicellular, yellowish 

 brown spines (figs. 47 to 49), whose colour presents a 

 contrast to tbe transparent marginal cell-walls, and to 

 the green contents of the cells of the lamina of the leaf. 

 The spines are acuminate, slightly curved, and gradually 

 narrowed from the base to the sharp point. 



VI. — The Leap-spines. 



The form of the spine, or tooth, on the margin oi 



the leaf furnishes good discriminating characters be- 



\ ft tween the various species of Naias, as was long ago 



Fig. 44. pointed out by the late Al. Braun in one of the earlier 



numbers of this Journal (vol. ii., 1864, pp. 274-279). 



The simplest form of tooth is that of N. fleoailis, where, in Dr. 



Boswell's Loch Cluny specimens, the base of the spine is in the 



same plane as the leaf-margin. The spine springs from a dilatation 



between two of the marginal leaf-cells (fig. 45), each of which nearly 



equally supports the spine to the extent of one-third its length, rarely 



more. Sometimes the two marginal cells are separated from each 



other by the spine (see fig. 46). 



Fig. 45. 



Fig. 46. 



Fig. 47. 



Fig.' 48. 



Fig. 49. 



In Naias grammea the type of spine is similar, but it differs from 

 that of N. flexilis in having a bi-celled base whose sides unequally 

 support the spine. The lowermost of the two basal cells diverges, 

 at its upper end, from the line of the leaf-margin, so as to wholly 



