34 NOTES ON PONDWEEDS. 



Although in its untypical forms this Potamogeton had been known 

 to me for about four years, until quite recently I was unable to refer 

 it to any named segregate of P. heterophyltus, nor to obtain any 

 definite suggestions as to its true specific rank from any of the 

 specialists to whom it was submitted. This difficulty no doubt 

 arose from the very untypical states the plant usually assumes in 

 the Huntingdonshire locality, and was only removed by the 

 development, in a single station, in the autumn of 1891, of a 

 form thoroughly characteristic of Fries' variety graminifoUus. 

 Fortunately I had been able to watch the very numerous forms 

 assumed by the plant throughout the fen, in preceding years, and 

 to gather complete series of each, illustrative both of inherent 

 variations and those consequent on frequently-changing external 

 conditions. So I had already been able to conjecture that these 

 very different-looking forms were in all probability stat*$ y rather 

 than true, persistent varieties, of one species ; a supposition amply 

 confirmed by the evidence furnished by the newly-discovered typical 

 form. This grew in a single patch spreading from one rootstock, 

 and in a station which favoured the development of many states 

 simultaneously. By patiently tracing out the stolons, they were 

 seen to ascend from deep to shallow water, and some even creeping 

 a little way up the bank became almost land-forms. By specimens 

 gathered from this siugle rootstock I was at once able to connect 

 the two extreme forms figured in Plate 317 as mere states of one 

 variable species. 



Iu the absence of special descriptions of the various forms 

 assumed by the Pidley Fen graminifoUus, its relationship to other 

 Fenland species will be most readily shown by detailing the steps 

 I took to ascertain its specific name, and, that being found, to see 

 whether any other Fenland Potamogetons could be ranged with it. 



In the first place, my attention was drawn to the typical form 

 above described (Plate 317) by a conspicuous autumnal stem 

 (growing in a station in which the plants had been observed for four 

 years), which, as it grew, looked so like the Irish "P. lonchitis" 

 that for a moment I felt sure it was that species. Although a 

 closer examination of the whole plant clearly showed that it was 

 only a large state of the heterophyll its-like species I had been 

 watching for years, I naturally compared my find with a set of 

 "P. lonchitis" from the Boyne. For want of any knowledge of 

 the completely submerged and younger states of the Irish plant, 

 the comparison was by no means complete, nor altogether 

 satisfactory to myself; as far, however, as it could be made, I was 

 unable to find, either in the fruit, general habit of the flowering 

 stems, or in the shape and structure of the leaves, any specific 

 difference between the two plants. But on further comparing both 

 sets of specimens with North American typical P. lonchitis collected 

 by Dr. Moron g, neither of them seemed to belong even to the same 

 natural section of the genus as the Amei'ican plant. 



Further than this, since the commencement of this note, I have 

 been able to compare all these plants with a beautiful series of 

 specimens received from Mr. Reginald Scully, labelled, "P. Zizii, 

 form, River Laune, Killorglin, Kerry"; with these both my plant 



