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forms a serrulate margin of the leaves might be expected 

 to be found, but as well in the Danish Potamogeton (25 B) 

 [Fig. 4, E] as in the specimens of P. undulatus of St. Peters- 

 bourg Museum, the leaves are quite entire as in P. praelon- 

 gus. The morphological as well as the anatomical propor- 

 tions thus seem to prove that P. undulatus is P. crispus x 

 P. praelongus. 



The Potamogeton found in England, and by English 

 Botanists referred to P. undulatus, differs from Wolfgang's 

 and our P. undulatus by its serrulate leaves, but Wolfgang 

 himself says, that the leaves have entire margins, and the 

 leaves of the specimens of St. Petersbourg Museum have 

 entire margins as those growing in Denmark. Moreover the 

 vascular bundles in the stem's bark are lacking in the Eng- 

 lish plant, but some strings are found just beneath the 

 epidermis as in P. perfoliatus. 



Finally the English plant has more, and more distant 

 strings in the axial cylinder than either P. crispus and P. prae- 

 longus, wherefore it can hardly be suggested to be a hybrid 

 between those, but it approaches very much to P. perfoliatus 

 both in the structure of the axial cylinder and in several 

 other characters , f. ins. the structure of the bark of the 

 stem , the habit and s. f . , and therefore I agree with Mr. 

 Fryer in considering it P. crispus x P. perfoliatus , but as 

 above mentioned, it cannot in that case be referred to P. un- 

 dulatus Wolfg. which is no doubt crispus x P. praelongus. 



In several places in East- and West-Prussia a Potamoge- 

 ton has been found, which perfectly agrees with the descrip- 

 tion of P. undulatus Wolfg. as well as with the Russian and 

 Danish specimens of it, and which has also been taken by 

 G a spar y (I.e.) for P. crispus x P. praelongus. Among the 

 Prussian specimens, which I have examined, was found one, 

 from Wiep-See, which hardly belonged to P. crispus x P. prae- 

 longus , the leaves being serrulated, in contrast to all the 



