SUPPOSED HYBRIDITY IN POTAMOGETON. 173 



Var. teres. — C, vulgaris var. teres Boott, iii. 168, (1867). From 

 Germany northward. 



Var. turfosa. — C. turfosa Fries, Summa, 228 (1846). C. vul- 

 garis var. turfosa Boott, iii. 169 (1867). Scandinavia. 



Var. bracteosa. — C. vulgaris var. bracteosa Bailey, Proc. Amer. 

 Acad. Arts and Sci. xxii. 81 (1886). California. Greenland. 



C. Gatulichaudiana Kunth, which Boott makes a variety of G. 

 vulgaris, appears, from the little material which I have seen, to be 

 at least a very doubtful variety of this species, and for the present 

 it had probably better stand alone. 



SUPPOSED HYBRIDITY IN POTAMOGETON. 

 By Alfred Fryer. 



When I first began to study local forms of Potamogeton in the 

 Fens, I was strongly prejudiced against regarding any of tbe 

 generally accepted species of authors as of possible hybrid origin, 

 but supposed tbat such species as are described in our standard 

 works were in all cases "good species," which especially fulfilled 

 the first tbeoretical demand of a species by being sterile with all 

 other species of the genus. If on rare occasions a cross ever 

 occurred, I held that the consequent offspring was absolutely 

 barren, and incapable of continuing its race except by " extension " 

 or growth from tbe original plant. Indirectly, these views were, 

 if I remember rightly, advocated in the earlier notes of this series. 

 By degrees, however, the local facts that presented themselves 

 compelled me to regard P. decipiens as a hybrid between P. lucens 

 and P. perfoliatus. This conclusion, by no means hastily made, 

 induced me more closely to examine the local distribution and life- 

 history of other so-called species of Potamogeton, and more espe- 

 cially to inquire into such circumstances as seemed to throw any 

 light on their origin, or the relationship they bore one to another. 



The facts observed in the course of these investigations, and the 

 conclusions I have arrived at, form the substance of this note. By 

 stating the facts fairly, I hope to enable the reader to correct for 

 himself any errors of inference I may have fallen into. 



In a previous note I stated that such forms as P. heterophyllus 

 and P. Zizii were as variable when growing apart as wben growing 

 together. This statement was altogether erroneous. I did not then 

 understand the difference between states of species and varieties 

 of species, — between forms that are only temporary and speedily 

 revert to the type, and forms that are permanent, for tbe life of tbe 

 individual at least. But continued study of the living plant of one 

 of our most apparently variable races of P. Zizii, showed tbat this 

 multiform plant has no true variety, inthe botanical sense of the word, 

 but tbat all its forms may be produced on the same rootstock, often 

 in a single season, or at most in the course of three or four seasons, 

 and that tbese forms are mere states due to temporary causes, such 



