v1] MARSH AND AQUATIC ASSOCIATIONS 159 
*Chara Braunti, *Naias graminea, and *Vallisneria spiralis. 
These, as has been recently shown, are confined to certain parts 
of the canal where the temperature is more or less permanently 
raised by the inflow of heated water from adjoining cotton mills 
(Weiss and Murray, 1909), and have no doubt been intro- 
duced with imported cotton. *Potamogeton pennsylvanicus, 
which, when first discovered in the canal at Halifax, was 
thought to be restricted to the water which is heated by the 
discharge from cotton mills (Bennett, 1908 a and 6), has been 
found to have a rather more extended range. This plant also 
has in all probability been introduced with cotton from North 
America. 
It is evident, therefore, that many water plants have ex- 
cellent means at their disposal for successful migration. Not 
only is this seen from the above-mentioned facts of distribution, 
but an experiment (Wheldon and Wilson, 1907: 339) confirms 
this well-established opinion. A pond was made, near Garstang 
in North Lancashire, in a grassy field to see which water plants 
would appear. The pond was carefully railed off to prevent 
access of cattle. After eighteen months, the following plants 
had appeared :—Witella opaca, Callitriche sp., Alisma Plantago, 
Glyceria fluitans, Juncus conglomeratus, and J. articulatus. 
It may, perhaps, appear surprising that practically no alien 
aquatic plants should have become established on the Pennines 
in the numerous reservoirs (see figure 36) which have been 
constructed at the clough heads during recent years; but the 
reservoirs are artificially kept clear of water “ weeds.” However, 
the only recorded station of the water purslane (Peplis Portula) 
in the Peak District is on the south side of the reservoir at 
Chapel-en-le-Frith (Linton, 1903: 151). 
The following is a list of the aquatic flowering plants of the 
ponds, mill-dams, canals, etc. of the southern Pennines. Most 
of the species occur only at altitudes below 600 feet (183 m.). 
Those which occur at the higher altitudes are indicated by 
the letter “U” (=upland) being placed in brackets after the 
specific name; and the plants that are not strictly indigenous 
are preceded by an asterisk (*):— 
