rcnihine to f;,vMr !ifo. Where the htimidily is hiph there ^ve 



the Frigid Zones. 'There the air is melodious wi'Ji the son-s 

 of birds, and the land teems with life. Where the hnmidity is 

 lowest there is a complete change in the plnnts and animril<=;, 

 the least life, and the stillness of death. There we find the 



varies so does the life, and so do the devices of self protec- 

 t'oii incrense inversely with the humidity. Since the humidity 

 of a region is governed by the proximity of bodies of water an'l 

 their size, by elevation, drainage, wind movement and the pres- 

 mcc ( r ab'^c'ice of Infty barriers which condense the air moist- 

 ure on one side or the other, we find it inexpedient to use hn- 

 nudity as a means of separating ihc life of regions geographic- 

 ; Ily or topographically. We therefore take the next lower 



Temperature is of two kinds, seasonal and annual. In the 

 Tropics at sea-level the temperature is alwavs above the mini- 

 mum growing temperature, and so the vegetation has to make 

 r.o provision of moment against such changes, but as we as- 

 cend the mountains or move -out of the Tropics toward the 

 roles all plants are subject to seasonal changes. In the Trop- 

 ics, though there are no temperature seasons, there is a period 

 of rest due to the lessened rains, called the drv season, and a 

 period of activity due to abundant rains, called 'the wet season. 

 In the Tropical deserts what there is of the wet season deter- 

 mines the growth of plants and has caused the highest develop- 



:e behind. All the protection the plant needs 

 ed which is so small that it will readilv pass 

 nto almost any crack, and be safely hid in a 

 Infting sand or settling dust, and because of 



appens that no moisture falls on the deserts 

 but It makes no dilTerence to the vegetation, 

 Ling the call of the livening showers. There 



