ON NAIAS GKAMINF.A DEL., VAR. DELILEI MAGNUS. 28 



in the stem, but much smaller and more circular (see fig. 89). 

 These cavities are regularly arranged in one series round 

 the central mass, as in the stem, but there are occasionally 

 outlying cavities in the neighbourhood of the external orange- 

 coloured cells, as shown in 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 re- 

 presented in Plate 249. These 

 Fia. 89. are generally given off singly from 



between the first pair of leaves of 

 the fascicle ; occasionally 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 intra-cellular 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 corre- 

 sponding 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 kind- 

 ness, to have the opportunity of seeing the plant in its station in 

 the canal at Beddish, near Manchester. The precise locality was not 

 intended to be published, but as the station seems to be well known 

 to so many local botanists there is no further need to suppress it. 



When I first visited the canal, on the 14th September, 1883, 

 the Naias grew in an area of about a quarter of a mile in length ; 

 in some portions of this space it was the prevailing plant, wholly 

 covering the canal-bed, while in other portions it was intermixed 

 with Potamogeton rufescens, P. obtusifolius, P. crispus, P. pusillus, 



