1915] 



WILLE — FLORA OF NORWAY 95 



* 



that these northern occurrences are of a distinct form (Picea 

 excelsa [Lam.] Link f. obovata Ledeb.), which is classed by 

 some botanists as a separate species, and has its distribution 

 through the north of Finland and Russia. There can, of 

 course, be no doubt that the spruces in these northernmost 

 occurrences immigrated independently from Finland, and 

 probably at a later period, as there is a tradition that they 

 were imported thither by human beings (Lapps). 



According to J. Holmboe, Calluna vulgaris came into Nor- 

 way during the same recent period in which Picea excelsa 

 made its appearance, but there is no doubt that the former 

 immigrated from the west and then spread eastward, i.e., in 

 the direction opposite to that in which Picea excelsa spread. 

 Both these species have now a very wide distribution in 

 Norway. 



Strange to say, there has not been found in the deposits 

 from the Pine Period in Norwegian peat-bogs a single plant 

 that is not to be found in the earlier periods. In Sweden the 

 only new species found is Rubus Chamaemorus, which, how- 

 ever, undoubtedly grew there long before, as it must on the 

 whole be considered to be a subalpine species. This is suffi- 

 cient to show that special conditions are necessary in order 

 that parts of plants may be preserved in bogs, and that it will, 

 therefore, always be only a small proportion of the plants 

 growing around the bogs which will be so preserved. 



It is strange, for instance, that Taxus baccata is not found 

 in Norwegian peat-bogs. It is found as a fossil from the Oak 

 Period in Sweden, and must have been far more common in 

 Norway in the early Iron Age than it is at the present time, 

 as H. Conwents found, on examining twenty-three vessels in 

 the Archaeological Museum in Kristiania, that eighteen of 

 them were of Taxus and only one of Picea excelsa. 



According to R. Sernander ('10) the period of greatest 

 warmth must have occurred in the Bronze Age, and he believes 

 that it was then that Corylus Avellana was most widely dis- 

 tributed northward. The Bronze Age, however, judging 

 from the molluscs that were then found off the south coast of 

 Norway, seems to have had a cooler climate than that of the 



