I/O THE SCOTTISH BOTANICAL REVIEW 



The Tertiary species Potamogeion getiicidatus, (Eningen, P. C(Bspitans, 

 Sap., Aix, seem to be satisfactory. 



The present distribution of Potamogetonacece favours the occur- 

 rence of Pofamogefon, Posidonia, Zostera, in the American Cretaceous 

 and European Tertiary. A number of species of Pota?>iogeto?i are to 

 be found in Preglacial beds, and Ihippia is met with in Interglacial 

 deposits. 



vi. Juncaginacecz. 



In the Tertiary of CEningen some fossils allied to Juncagmeae are 

 found, which Heer, basing the determination upon the fruits, which 

 he considers related to Scheuchzeria, names Laharpia umbellata. 

 The present distribution of Scheuchzeria is confined to North and 

 Mid Europe (Arctic), North Asia, and the Rocky Mountains, and 

 the genus is represented by one species only, S. palustris, L., with 

 a creeping root-stock, slender leaves, flowers in a raceme, and 

 fruits of 2-3 follicles. It is found in beds of late Glacial and 

 Neolithic age in Sweden. 



vii. Aiisfuacetz. 



The Alismacese are aquatic or marsh plants. To this group 

 several fossils of Upper Cretaceous or Tertiary age are assigned. A 

 fossil named Alismacites primcevus, from the Wealden of Portugal 

 may possibly be correctly assigned. Some are compared with 

 Alisma, a genus with erect leaves, whorled flowers, and erect seeds 

 with a hooked embryo. 



Such plants as those described by Heer from Atane, under the 

 name Alisma reticulatuin^ cannot be determined. The attribution 

 of A. macrophylhi7n to Alisma is doubtful, and the fossil described as 

 A. paucinervis may even be dicotyledonous. The former is a 

 Spitzbergen species, the latter from Greenland, which demonstrates 

 the former wide Northern distribution of the genus, now common to 

 the Temperate and Tropical zones. All of these fossils are based 

 upon leaves, and in a fossil condition there cannot be much to 

 distinguish the leaf of an Alisma from that of a Potafnogeton. 

 Indeed A. lancifoliutn of the Eocene may belong to the latter. 

 Alisma plantago, L., occurs in Preglacial beds in Britain. 



Sagittaria is another genus of similar habit and much the same type 

 of inflorescence as Alis7na, from which it differs in being unisexual. 

 The fossil from Alaska, described by Heer as Sagittaria pulchella^ 

 is quite likely to belong to Potamogetofi or Alisma. The fossils 

 founded on characters of the fruits, which in the recent genus 

 resemble those of Alisma, viz. S. difficilis, S. hyperborea, described 

 by Heer from the Tertiary of Spitzbergen are exceedingly doubtful. 

 The recent genus is distributed over the temperate and tropical 

 zones. 



It is found in Interglacial beds in Britain and in Neolithic beds 

 in Sweden. 



]t is conceivable that many fragments of totally distinct plant 



