138 NOTES ON PONDWEEDS. 



this view is not supported by its local distribution, nor by its leaf- 

 structure and habit of growth, which latter is that of P. perfoliatus. 

 This origin is also rendered highly improbable by the early flower- 

 ing of P. pralongus, which is usually in fruit by the time the first 

 flowers of P. lucens begin to expand. 



Although mature fruit of P. decipiens is never produced, yet 

 isolated plants which are apparently seedlings are not unfrequently 

 found in remote localities, to which it is almost impossible that off- 

 sets of living plants could be carried by natural means. In 

 these situations a single plant only is usually found, which often 

 presents some slight individual peculiarity sufficient to distinguish 

 it alike from the type, or from other local forms. These plants are 

 always found growing with the supposed parents ; I have never 

 met with them in localities where lucens and perfoliatus were not 

 present. In waters where P. decipiens grows more abundantly it 

 occupies large spaces or beds, evidently by the extension of the 

 strong- growing rootstock ; each of these beds is composed of plants 

 which do not vary year after year, but it will often happen that three 

 or four beds, each tenanted by a slightly differing variety, occur in the 

 space of a few yards, too near for local causes to produce variation, 

 and yet so constantly distinct as to induce the belief that each bed of 

 plants is the produce of a different seed. Under cultivation, as far 

 as I have been able to observe, local forms of P. decipiens remain 

 very constant, which is not the case with those of some species of 

 Potamogeton. Although these facts are not conclusive proofs of a 

 hybrid origin for P. decipiens, they present an accumulated weight of 

 evidence which is difficult to rebut. 



Before I thoroughly knew this plant I frequently passed it 

 over in its early states as P. luccns, or when in flower as P. per- 

 foliatus. It resembles the latter species in the lower stipules ex- 

 panded into ear-like leaves towards the tip, and in the lower leaves, 

 which are narrow and slightly stalked in both species, although rarely 

 present in this state. The alliances, and probably the origin, of 

 the species of Potamogeton must be sought in their early stages, 

 which often present features which entirely disappear with the 

 growth of the plant. Thus stipules with adnate leaves are 

 frequently met with on young steins of most species of Potamo- 

 geton, while in P. pectinatus, belonging to a group characterised by 

 adnate leaves, the lower leaf is often merely sessile ! 



I am indebted to Dr. Tiselius, of (Stockholm, for a very 

 beautiful series of Swedish forms of P. decipiens, and he expresses 

 a very decided opinion that this species is the same as P. sali- 

 cifolius of Wolfgang, of which he possesses an original specimen 

 which agrees in all respects with a form named by him P. upsali- 

 ensis. Dr. Tiselius labels a plant which is exactly like our fenland 

 decipiens, 



" Potamogeton upsaliensis Mihi. 



— salicifolius Wolfg. 



= lithuanicus Gorski. 



= lanceolatus Reich, non Sin. 

 Omnes formae P. decipientis Nolte." 



