4 
points project, or narrow bands curve to follow the sinuosities of 
the mountain sides. The peculiar topography of this state produces 
a variety of life zones which is probably equaled by no other similar 
area elsewhere. Bordered as California by the sea; traversed its 
whole length by a mountain range, in places carrying perpetual snow ; 
possessing considerable areas lying below sea level; having a range 
of annual rainfall varying from 8o inches in the northwestern part 
of the State to 3 or 4 in the southeastern part, it offers the student 
of chmatology and of the distribution of life facilities unsurpassed 
in any civilized country, and problems unknown in most other parts 
of the world. 
Long ago geographers divided the earth’s surface into five zones, 
giving them definite boundaries of certain parallels of latitude 
founded on astronomical considerations. Biologists have also divided 
the earth’s surface into life zones and other divisions. ‘These divi- 
sions seldom have very definite boundaries, but blend into one another. 
For my present purpose I shall follow the division of the northern 
hemisphere into three Life Realms, as follows: The Arctic Life 
Realm, surrounding the north pole and passing southward to the 
northern limit of trees, or about the annual isotherm of 32 degrees; 
the North ‘Temperate Life Realm, extending southward from the 
Arctic Life Realm to about the annual isotherm of 70 degrees; and 
a Tropical Life Realm. ‘These Life Realms are subdivided into Life 
Zones as follows: An Arctic Life Zone, consisting of all the Arctic 
Life Realm; a Boreal Life Zone consisting of the upper or northern 
part of the North Temperate Life Realm south to about the summer 
isotherm of 63 degrees; a ‘Transition Life Zone, consisting of that 
part of the same Realm bounded above or on the north by the 
summer isotherm of 63 degrees, and below! or south by the summer 
isotherm of 70 degrees; an Upper Austral Life Zone lying between 
the summer isotherms of 70 degrees and 77 degrees; a Lower Austral 
Life Zone consisting of the remainder of the North Temperate Life 
Realm; and a Sub-Tropical Life Zone consisting of the northern 
part of the Tropical Life Realm. ‘This covers but a small area in 
southeastern California. ‘That part of the Arctic Life Zone in Cal- 
ifornia is still smaller, consisting of a few small isolated areas on the 
highest mountain summits. 
The distribution of life being affected also by the greater or less 
average amount of moisture present in a given area, and as this 
