72 MR. C. BAILEY ON THE STRUCTURE ETC. 



waters the meclianical cells would become deprived of 

 their functions. Thus we find Schwendener^ in his ex- 

 haustive work, ' The Mechanical Principle in the Anato- 

 mical Construction of Monocotyledons/ Leipzig, 1874, 

 page 122, remarking that Potamogeton fluitans in its cus- 

 tomary habitat of running water has a developed system 

 of bark-bundles, whereas the var. /8 stagnalis, Koch, is 

 completely deprived of same, 



" The var. Delilei, found in the stagnant waters of the 

 overflowed Nile, is a most persistent and constant one, as 

 during a period of a hundred years it has been indubitably 

 collected by Delile, Schweinfurth, and Ehrenberg in Lower 

 Egypt. Its unaltered appearance in England and in the 

 oases shows its constancy and total independence of 

 habitats, whilst its formation has probably been caused by 

 the same.''^ 



It now only remains to me to tender my acknowledg- 

 ments to Mr. Ridley, Mr. Arthur Bennett, Dr. Magnus, 

 Professor Ascherson, Mr. Beeby, and Mr. James Britten, 

 for their kind assistance during the preparation of this 

 paper. 



XX. Explanation of the Figures. 



Plate IV. 



Fig. I. The upper portion of a branch oi N. graminea, from Reddish; nat. 

 size. 



2. Two of the leaves from same, drawn rather broader than the natural 



size, the sheaths and auricles flattened out. 



Plate V. 



3. Upper portion of a branch of N. graminea from Lower Egypt. 



Copied from Delile's drawing in his 'Flore de I'Egypte,' but 

 reduced to two thirds original size. 



4. Base of a leaf -fascicle, showing leaf-auricles, fruits, &c. ; slightly 



enlarged. From Delile's ' Flore de I'Egypte.' 



5. Section of fruit; enlarged. From Delile's 'Flore de I'Egypte.' 



