SUPPOSED HYBRIDITY IN POTAMOGETON. 175 



produced floating leaves, but gradually extended itself year by year 

 until it began to form a little colony or bed sufficiently strong to 

 keep out other forms of the genus from intruding on its territory. 

 Its exact station was sufficiently fixed in my memory by the fact 

 of its occupying a clear space of water between two local forms of 

 P. Zizii and P. keterophyllus. In June of 1889 I visited this drain 

 for the first time that season, and was greatly surprised to see a 

 new form of Potamogeton quite unknown to me. I thought I knew 

 each individual plant in Broker's Drain as well as I knew each in- 

 dividual face in the circle of my friends, for I had watched and 

 gathered specimens of each local form and of almost every indivi- 

 dual plant for four or five years, yet here was something quite new 

 and which I could not refer to any segregate known to me. 

 Hastily fishing a plant up, the lower leaves of the stem at once 

 showed that it was the supposed seedling I had referred to P. 

 fluctuans. The next point was to make sure of the exact locality 

 by examining the plants on either side, and I found the beds of 

 Zizii and keterophyllus, both of which I know perfectly well. Now 

 this new form of P. fluctuans was not like the other forms I had 

 referred to this segregate, except in the lower leaves, but was 

 curiously intermediate between the local forms of P. Zizii and 

 P. keterophyllus which grew on either hand. Perhaps it is hardly 

 possible to obtain a stronger proof of a natural hybrid or cross- 

 bred plant than this instance affords. It seems to me only less 

 strong than would be the case if such a form had been obtained 

 artificially, by actually crossing the Zizii and keteropkyllus-fovms. 



Unfortunately the drain was cleared of weeds in the ensuing wet 

 July, before the plant had time to produce fruit, which, I think, from 

 the appearance of the abundant flower-spikes, it would have done. 



The original Scandinavian form, named by Dr. Tiselius, " P. 

 keterophyllus Schreb. v. fluctuans mihi," certainly fruits readily. I 

 have always considered it to be a hybrid between keterophyllus and 

 Zizii, approaching more nearly the former plant. I sent Dr. Tiselius 

 one of the forms from Broker's Drain, labelled " keterophyllus x 

 Zizii" on which his comment is, " resembling fluctuans T is.," . . . 

 " possibly Zizii x keterophyllus (as) observed by you." This second 

 fluctuans-fovm. fruits freely with us, but perhaps less so than either 

 of its supposed parents. 



Having thus convinced myself that these two forms, P. Zizii and 

 P- keterophyllus, do interbreed, I next turned my attention to the 

 local circumstances in which P. varians grows, and to the variations 

 it undergoes, both independently of, and in connection with, those 

 conditions. I had previously suspected the hybrid origin of P. 

 varians, as my published note on that segregate will show,* but now 

 I began to push my researches in a fresh direction with some degree 

 of confidence. This was to observe whether any variation had 

 resulted from propagation by seed, or otherwise, in a colony of P. 

 varians which grew apart from both Zizii and keterophyllus, and 

 offered an unusually favourable opportunity of seeing what a single 

 plant of a supposed hybrid would do when left to itself. 



* Journ. Bot. 1889, 35. 



