222 



II. Temperate Zone, This is also usually sub -divided 

 into the Warm Temperate and Cold Temperate 

 Zones. 

 III. Arctic Zone. This is sometimes divided into the 



Sub -Arctic, Arctic and Polar Zones. 



The Zones in the northern hemisphere are usually termed 

 Boreal and those in the southern hemisphere Austral. 



The Tropical Zone is characterized by possessing Palms, 

 Bamboos, Bananas, Tree Ferns, Cycads and Screw 

 . j. Pines (Pandanus), while the most important forest 



t trees in this Zone, in India, belong to such natural 



orders as Leguminosae, Dipterocarpaceae, Combre- 

 taceae, Urticaceae, Meliaceae, Verbenaceae, Guttiferae 

 and others. 



In the Temperate Zone the most important forest trees 

 belong to the Coniferae and Cupuliferae, the latter in- 



cluding the Oak, Beech, Chestnut, Hazel, Hornbeam, 

 Birch, and Alder. Other characteristic trees are the 

 Poplar, Willow, Elm, Walnut, Maples, and Holly, 

 while among shrubs, Berberis, Rhamnus, and Euony- 

 mus, are common. One of the most typical 

 natural orders is perhaps that of the Rosaceae. 

 The Arctic Zone. The species found in the cold tem- 

 perate zone also extend into the arctic zone, but, in 

 the latter, there are fewer species, and the vege- 

 i tation is especially characterized by being stunted. 



The limit of tree growth is usually regarded as the 

 natural boundary of the arctic zone, in the latter 

 the trees becoming shrubs, while shrubs and herbs 

 are much reduced in height. Plants in this zone 

 usually have small leaves and well-developed roots, 

 while large and brightly coloured flowers are 

 common. 



Although the above suffices to illustrate in a general way the 

 of Tempera- importance of temperature as a factor influencing the distribu- 

 ture. t ion of plants, it must be borne in mind that the mean annual 



temperature is very much less important than the extremes of 

 temperature in any locality, and also that the effect of a certain 

 temperature on a particular plant depends largely on the season 

 of the year and the stage of development of the plant. Some 

 plants require high temperatures throughout the year, others 

 uniformly cold temperatures, while yet again others require high 

 temperatures at certain seasons and low temperatures at others. 

 Thus although the temperature in a given locality may be 



