

66 ANNALS OK THE MISSOURI BOTANICAL GARDEN 



[Vol. 2 



55') ; but it is nowhere known to have reached a greater 

 height above sea-level than 1.722 feet. 



The oak can stand a winter temperature as low as — 33.8° 

 C, but requires a mean summer temperature of 12.6° C It 

 is now comparatively rare, and seems to be decreasing. It 

 occurs in large quantities only on the Silurian and along the 

 lower parts of the coast. 



A number of deciduous trees that are susceptible to cold 

 have about the same distribution as the oak, both in height 

 and in northward extension. These are: Acer platanoides, 

 Alnus glutinosa, Betula verrucosa, Crataegus Oxyacantha, 

 Fraxinus excelsior, Prunus avium, P. insititia, Pyrus Mains, 

 Sorbus Aria, 8. fennica, Taxus baccata, and Tilia cordata. 

 There are also a number of species of cryptogams. It may 

 on the whole be said that the zone here designated the Oak 



Zone is that of Norway's most abundant flora. 



Within the Oak Zone, large districts may in their turn be 

 marked off that possess a characteristic flora, the occurrence 

 of which is especially conditioned by circumstances of tem- 

 perature and soil. 



1. The Region of the Silurian Flora. — This is developed in 

 an especially characteristic manner on the calcareous slate 

 along the Langesund Fjord, the west side of the Kristiania 

 Fjord, in Eingerike and Hadeland, and around Lake Mjosen. 

 In some of these districts it is fairly cold in the winter, but 

 very hot in the summer; 1 and as the soil is calcareous and 

 warm, a xerophilous steppe-flora, with its characteristic 

 Labiatae, Boragineae, and Centaurea species, and thistles, 

 such as Carlina vulgaris, Carduus acanthoides, etc. — species 

 which also occur in the steppe-regions of South Russia, can 

 thrive well on southern slopes. 



For the rest, the flora is rich in characteristic species, e.g., 

 Artemisia campestris, Brachypodium pinnatum, Carex prae- 

 cox, Cephalanthera rubra, Cirsium acaule, Fragaria collina, 

 Libanotis montana, Ononis campestris, Phleum phalaroides, 



1 In Kriatiania, the 30-yeara' average minimum atmospheric temperature for 

 the month of January in — 16.5°C, and the average maximum for the mouth of 

 June -|-28.9 C. 



