800 THE JOURNAL OF BOTANY 



folius Fryer). — P. sparganiifolius Bab. non Laestad. (P. Kirkii Syme) 

 is believed by Fryer to be probably P. natans x polygon i/olius. 

 P. Griffithii Bennett is certainly a hybrid, fide Fryer (P. polyyoni- 

 folius x ?) ; it is P. alpinus x prmlongus according to Ascherson & 

 Graebner (Syn. Fl. Mitteleurop. i. 1897, p. 317), but Mr. Bennett 

 still holds it to be a species, remarking that P. pralongus is not 

 known for Carnarvon, and has only one station in Anglesea. 

 P. Drucei Fryer (P. natans X alpinus?). — P. heterophyllus x P. 

 coloratus (P. gracilis Wolfgang). — P. lanceolatus Sm. On this Mr. 

 Fryer writes to me : " Certainly a hybrid. No two forms of this 

 from different localities are alike. Our Cambridgeshire form is 

 P. heterophyllus X Friesii, and deserves a segregate name. Smith's 

 plant (i.e. the Anglesea plant) is evidently P. heterophyllus x pusiilus. 

 I am inclined to assign the same origin to the Irish form. And 

 he adds that he is strongly inclined to think that local pecu- 

 liarities in a parent plant are imposed on its hybrid offspring. 

 P. rivularis Gillot (P. heterophyllus x pusiilus ?), fide A. Bennett, 

 who gives me P. lanceolatus Sm. as = P. heterophyllus X Friesii ? 

 P. heterophyllus x natans (P. Tiselii Richter). — P. falcatus is put 

 to P. heterophyllus (subgramineus) x nitens f3 falcatus by Asch. & 



Graebner (I. c. p. 328). Mr. Fryer, who does not offer this or any 

 other solution, remarks, in litt. 9 "It has kept its characters for 

 many years in the original locality, and also under cultivation 

 until it fruited. " — P. nitens Web. Mr. Fryer considers to be always 

 a hybrid of varied parentage, and questions whether it ever bears 

 more than an occasional perfect fruit, never a fruiting-spike. Mr. 

 Bennett ascribes it to P. heterophyllus x perfoliatus. — P. lucens x 

 pr&longiis (P. Babingtonii Ar. Benn., P. longifolius Bab. non Gay). 



— P. lucens x perfoliatus (P. decipiens Nolte). — P. decipiens Nolte 



var. atfinis Ar. Benn., Mr. Bennett now thinks is probably P. 

 decipiens x nitens — P. Brotherstonii Ar. Benn. MS., but (he adds) 

 Asch. & Graebner (p. 830) place it under P. perfoliatus x lucens 

 (P. decipiens p. pte.). — P. salicifolius Wolfgang (the Herefordshire 

 form) is thought by Mr. Fryer to be a hybrid of unknown origin. 

 Mr. Bennett believes Wolfgang's plant to be P. alpinus x lucens.-— 

 P. angustifolius x heterophyllus (P. varians Morong ex Fryer). — P. 

 anyustifolius X coloratus (P. Billupsii Fryer). — P. jjralongus x poly- 

 goni folius (P. Macvicarii Ar. Benn. Ann, Scott. Nat. Hist. 1907, 

 106). — P. crispus X perfoliatus (P. Cooperi Fryer and var. Jacksoni 

 Fryer). — P. crispus x pralongiis (P. imdulatus Wolfgang), see paper 

 by Ar. Bennett (Jww. Scott.' Nat. Hist. 1907, 104). — P. crispus X 

 obtusifolius (P. Bennett ii Fryer). — P. wisptts x Friesii (P. Lintoni 

 Fryer). I have remarked above on the general sterility of the 

 hybrids of this genus. It is not impossible that sterility is the 

 universal rule here, and that the exceptions are due to fertilization 

 by the pollen of one of the parent plants. For Mr. Bennett on 

 this point observes that "in many (hybrids) the flowers do not 

 open, and in others, when they do, the pollen is bad. ,J If this is 

 always the case, we cannot attribute fertilization to the hybrid, 

 and can hardly do otherwise than fall back on a parent plant for 

 the male element. 



