ON NAIAS GRAMINEA DEL., VAH. DELILEI MAGNUS. 



9 



support the lower end of the spine (see fig. 47). The uppermost 

 cell, on the other hand, acts as a support to the inner side of the 

 spine for fully one-half its length; it also partially underlies the 

 upper end of the lowermost basal cell, and thus its three-sided profile 

 fills up the axil of the spine and adds considerably to its rigidity, as 

 compared with the arrangement in N. flexilis (comp. fig. 45). Oc- 

 casionally a third cell makes its appearance, as shown in fig. 48, and 

 not infrequently there is an auxiliary spine between the upper sup- 

 porting cell and the original spine (see fig. 49). In all these cases, 

 however, the axillary, or uppermost, basal cell distinguishes the type 

 of tooth from the characteristic tooth of N. flexilis. Cesati gives 

 figures of the dentition of these two species in Plate II. of ' Linnffia,' 

 vol. xxxvi. ; but he makes that of N. alaganensis much nearer to that 

 of N. flexilis than I find it to be in the Manchester plant. 



A third type of spine is furnished by Naias minor 

 All. (Caulinia fragilis W.). This shows an advance 

 upon the basal arrangement of the spines of N. flexilis 

 and N. graminea, in being formed of more than three 

 cells (see fig. 50). The entire tooth stands much above 

 the line of cells which forms the margin of the leaf. 



Upon comparing these figures (which I have care- 

 fully made from typical specimens) with those given by 

 Braun on p. 275, vol. ii. of this Journal, it will be seen 

 that my drawings present considerable variation from 

 his, particularly in N. flexilis. It is possible that 

 Braun's figures were meant to be diagramatic, and 

 representative of groups rather tban of species ; for 

 convenience of reference I have reproduced them in 

 Plate 251, figs. 6 to 8. 

 The other end of the series of types of spines is represented 

 by the tooth of N. major, where there is not only a multicellular 

 base, but the spine itself is compound-; one terminal dark brown 

 cell resting upon several elongate dark brown cells, the whole 



forming a very conspicuous tooth 

 standing well out from the plane of 

 the leaf-margin. Fig. 51 gives a 

 tooth of this species from one of the 

 late Dr. Wirtgen's specimens from 

 the mouth of the Moselle, near 

 Coblentz. 



In N. graminea the spines are 

 situated on the leaf-margins only 

 (never on the midrib) at intervals 

 equal to from one-half to the whole 

 breadth of the leaf. Figs. 47 to 49 

 have been drawn" from spines on the 

 edge of the middle portion of the leaf. 

 Their shape is constant on the sides 

 of the lamina, but they become longer 

 oh the sheath, and at the apex of the 

 leaf. 

 Fig. 51. 



