60 MR. C. BAILEY ON THE STRUCTURE ETC. 



fore appear that the sculpture of N. fiexilis is quadran- 

 gular, while that of N. graminea is hexagonal ; but too 

 much must not be made of observations founded on such 

 a limited basis. 



According to the observations of Cesati"^ the fruits of 

 the Italian N. alaganensis are granulose -punctate, which 

 fairly well describes the appearance of the outer covering 

 of the Manchester plant ; but Cesati^s figure in ' Linnsea/ 

 I. c. table ii. fig. 2d, makes the fruit much more papillate 

 than I find it in the Lancashire form. On the other hand, 

 this same observer makes the fruit of N. flexilis shining 

 and obscurely angular, and he so draws it in his plate. 



The explanation of this difi'erence in the form of sculp- 

 turing is probably due to the fact that the external mem- 

 brane more or less obscures the underlying layer, and thus 

 the latter is seen by observers according as the trans- 

 parency of the outer layer admits of it. For the further 

 elucidation of this point, I have reproduced the figures of 

 Dr. Magnus in Plate YII., where figs. 40 & 41 show the 

 arrangement of the coats of the fruit of N. graminea from 

 Cairo, and figs. 37-39 those of N. fiexilis. 



At Reddish mature fruits of N. graminea are produced 

 in great abundance; scarcely a plant occurred without 

 fruits. In the many hundred plants which I have examined 

 I have not seen a single instance where the beak of the fruit 

 was other than bifid, unless it had broken off" altogether, 

 as represented in figs. 81 & 83, and in the middle fruit of 

 fie:. 86. This division of the beak into two branches is a 

 constant character, and very clearly distinguishes it from 

 the four-rayed beak oi Naias flexilis (fig. 87). 



One other point of differentiation between Naias gra- 

 minea and N. flexilis rests in the shape of the fruit. In 



* " Die Pflanzwelt im Gebiete zwisclien dem Tessin, dem Po, der Sesia 

 uud den Alpen" (Linntea, toI. xsxii. 1863, pages 259 & 260). 



