OF NAIAS GRAMINEA, VAR. DELILEI. 63 



fig. 89. Enclosing the whole is a layer of larger- sized 

 cells of a dark brown colour, and more angular in outline 

 than any of the other cells. In the midst of these cells, 

 but on the outermost side, are a few cells filled with a rich 

 tawny-brown pigment. The walls of the circumferential 

 cells are all very thin, and they have the rich colour of the 

 pigment-cells. 



In addition to the roots proper the plant gives off 

 adventitious roots from the stem-nodes, as represented in 

 Plate IV. These are generally given off singly from 

 between the first pair of leaves of the fascicle ; occasion- 

 ally two proceed from the same node, but in such case the 

 second root emerges on the opposite side of the node. In 

 the lower portions of the stem the adventitious roots 

 become more numerous from each node, and they begin 

 to acquire the orange colour of the roots proper. They 

 attain a length of from half an inch to six inches or more, 

 and they have a similar internal structure to that of the 

 roots proper ; the peripheral cells, however, do not possess 

 the angular character nor the tawny colour of the outer 

 layer in the lower roots. The tissue is more loosely 

 aggregated ; the intracellular cavities are fewer in number 

 and smaller, scarcely exceeding the size of the cells which 

 surround them. The central cavity is present, as well as 

 the surrounding sheath, but the cells of the latter are 

 fewer than they are in the root proper. The external cells 

 do not differ much from the inner cells either in shape or 

 in colour, the rich pigment of the corresponding layer in 

 the root being absent. 



XVI. The Lancashire Locality. 



The occurrence of a Naias in Lancashire was so 

 unexpected a circumstance that I was pleased, through 

 Mr. Whitehead's kindness, to have the opportunity of 



