Ix POTAMOCrKTON BENNETTII. 



totally uulike each other in facies, and in P. Bennettii the lower 

 leaves are sessile, not mounted on stipules, as many of them are in 

 P. crispns, and are narrowly linear. 



Although our plant cannot be placed under the form assumed 

 by Syme to be the P. serratus of Hudson, it probably is identical 

 with one described by Kegel and Maack as P. serrulatns. In the 

 absence of type-specimens I can give no opinion on this matter ; 

 but in any case Mr. Bennett tells me that the name serrulatus must 

 be abandoned as having been previously used in the genus. 



The following description [TenUmien Florae Ussnrienfiis) accords 

 well with our plant, except that the leaves are there described as 

 3-5-ribbed, whereas in the British form the leaves seem to be 

 uniformly 3-ribbed only :— 



"467. PoUiiiwi/ctun serrulatus Kgl. et Maack ('?): foliis omnibus 

 submersis, membranaceis, pellucidis, sessilibus, exacte linearibus, 

 obtusis, 3-5-nerviis, margine sub lente argute serrulatis. 



" Specimina Maackiana floribus fructibusque carent. Habitus 

 omnino /-'. ohtuaifoUi, folia autem sub lente tenuiter argute serru- 

 lata. 



" In dem Gebirgsbache Damagu auf der rechten Seite des 

 Sungatschi. 



" Wir hielten die vorliegende Art anfanglich fiir P. ohtusifoUus, 

 von welchem sie sich jedoch gut unterscheidet. Bis aber Exemplare 

 mit Blumen oder Friichten bekannt sind, muss diese Art noch 

 zweifelhaft bleiben, da es immerhin moglich, dass solche auch nur 

 die submerse Form einer andern Art darstellf {i.e. p. 139). 



Tlie above might well stand for a description of our British 

 plant in its earlier stages of growth. Now that we are fortunately 

 able to supply the flowering state demanded, the relationship to P. 

 crispus becomes evident ; but I think it is no less evident that the 

 species is almost equally allied to P. obtusifoliufi. It cannot, how- 

 ever, be referred to either species, and having regard to its structure, 

 habit, and, above all, to the inflorescence, it seems difficult to avoid 

 the conclusion that P. Bennettii is a hybrid between P. crispus and 

 1\ (ihtusifoiius. 



The merit of the discovery of this most interesting plant in 

 Great Britain is due to Mr. R. Kidston and Col. Stirling, who 

 found it in tbe early state in 1890 at Grangemouth, Stirlingshire. 

 Following up the clue then obtained, they patiently examined tbe 

 locality again and again, until perfect specimens rewarded their 

 research. Perhaps it may not be out of place to give extracts from 

 tlie notes in their herbarium, made by Mr. Bennett and myself 

 before mature examples of the plant had been found, especially as 

 these conflicting opinions well serve to illustrate the diverse and 

 obscure character of the species in its early state. 



The first specimens were labelled by Messrs. Kidston and 

 Stirling, "P. obtusifulius M. et K. Wood Pond, Grangemouth, 

 R. K, & J. S. S., 17.8.(18)90." On these Mr. Bennett wrote:— 

 " Two specimens of this are both P. crispus L. ! I expect you will 

 rather demur to this, but it is so ! Exactly similar specimens are 

 in Mr. H. C. Watson's herb, at Kew, from Surrey, and named 



