oa Botanical Geography. | 439 
Dependent on these conditions, the whole of this forest- 
region from the Atlantic to the Pacific Ocean may be 
divided into seven zones :—1, the French zone of the sweet 
chestnut ; 2, the German zone of Pinus Ficea; 3, the 
Eecanatian zone of Quercus Cerris; 4, the central Russian 
zone of exogenous forests ; 5, the “hontneen zone of Coni- 
ferze; 6, that of Quercus ae ; and 7, that of Betula 
ewan? 
- Among all the forest-trees of Europe the beech is the 
most characteristic of a maritime climate ; but the zone of 
the beech passes gradually into those of the chestnut, Pezus 
Picea, and Quercus Cerris. These three zones correspond 
to particular districts of the maritime climate characterised 
by the difference in mean temperature between the coldest 
and warmest months of the year. In the first zone, the 
mean monthly temperature varies between 12°°5 and 17°°5 C. ; 
in the second between 17°°5 and 22°°5 ; and in the third 
between 22°75 and 23°°5 C. The characteristics of the. 
central Russian zone of exogenous trees, of the northern 
zone of Coniferze, and of that of Quercus mongolica, depend 
on their continental separation from the influence of the 
ocean. The broad girdle of forests of the Russian lowlands, 
which consist mainly of oaks, is limited on the north by the 
: decreasing temperature, on the east by the insurmountable 
barrier of the Ural mountains. ‘To the north of it is found 
therefore a belt of Conifers—pines and larches—accompanied 
_ by birches, which reaches to the Arctic Region, and across — 
the Ural through Siberia, till at length it reaches the Amoor 
and the sea-coast of Ochotsk. ‘The zone of the Amoor or 
northern Mantschuria has a completely continental. cha- 
racter. The trees, among which Quercus mongolica is the 
most characteristic, belong for the most part to European 
genera, but to peculiar species ; the Siberian Coniferz occur 
_ here only on the mountains. The last zone, that of Betula 
_ Lrmamni, owes its peculiarity—a long period of vegetation ~ 
with a diminished summer temperature—to the neighbour- 
