276 



NOTES ON PONDWEEDS. 



miles before their floating cradle is arretted by some obstruction in 

 the water or by the shore itself. Many seeds and delicate " winter- 

 buds " of plants that could not vegetate in the cold depths to which 

 tbey accidentally sink are thus brought within reach of light and 

 and warmth. To such an extent is this transportation of the 

 floor- life of stagnant waters carried, that I have seen ditch-bottoms 

 that were completely hidden with Alga* early in spring, bright and 

 clean by Midsummer. It is especially instructive to see beds of 

 bivalve mollusca, such as Cyclas, rise and float away. Distribution, 

 "cross-fertilization," and 'change of soil, are all secured by this 

 simple means for the most inert forms of lower life. 



But to return to the subject of this note :— Through the kind- 

 ness of my friend, Mr. Arthur Bennett, I possess a very similar 

 plant to the autumn state of P. fluitcms, but with the addition of a few 

 floating coriaceous leaves. This specimen was gathered in Sweden 

 by Dv. Tisehus in 1881, and doubtfully referred by him to P. 

 HuiUms, a name in which Mr. Bennett did not concur. Afterwards 

 iJY. Tisehus suggested that this plant might be a hybrid between 

 / . nutans and t\ heterophyllm, and that it was probably the same 

 lorm as Messrs. Linton's Irish " P. sparganifolius:' 



Ihese suggestions of the learned Swedish botanist, who is one 

 ot the greatest living authorities on the genus Potamogeton, bring 

 us to the consideration of the specific rank and alliances of 

 1 . fluUan*. Is it a hybrid ? Or does it differ sufficiently from other 

 turnis of the genus to entitle it to specific segregation, and where is 

 it3 place m the genus ? 



In favour of the first question : the flower-spikes are usually 

 barren, perhaps always so in our British plant, of which no certainly 

 lertile fruit has yet been seen ; the plant is also of extraor- 

 dinarily vigorous growth, and can propagate itself readily by other 

 means than seed; further than this, in facies it is considered by 

 some botanists to be intermediate between P. nutans and forms of 

 r. ween* ; and also it has never been found in this country except 

 m waters where these two species grow. 



Un the other hand it may be urged that barrenness is no proof 

 oj Uybndity in the genus Potamogeton ; nor does the fact that a form 

 or potamogeton has never been known to produce seed make it 

 probable that it will not, under favourable conditions, ripen seed 

 abundantly. The Eev. Thomas Morong tells me that P. variam 

 lias never ripened its fruit in America, although carefully observed 

 lor lorty years. In England it ripens its seed freely. P. ZuU too, on 

 me same authority, is always barren in some of the North-American 

 lHKes, in others it is fertile. Here in the Fens it is always abun- 

 aantly fruitful, except in one isolated locality, where I have never 

 seen it produce even a flower-spike. Again, for how many years 

 ^as iruit of P. lanetolatu* (one of the best and most distinct 

 species of Potamogeton known) sought for without success ? We 

 uave, therefore, some reason to suppose that our English form of 

 i . mtawm&j ultimately be obtained in a fruiting condition, just 

 as uie Continental form of the species (closely agreeing with ours!), 

 Hiougb usually barren, is sometimes obtained in good fruit. 



