2nd, Climatic factors. 
3rd, Biotic factors. 
Fore Ee hiysical “factors. 
re, Water. 
a. Majority of piants need perceptibly moist soil. 
b. Certain plants adapt themselves to dry con- 
ditions. 
By enlarged root system. 
By reduction of leaf surface. 
c. Certain adapt themselves to wet conditions. 
By reduction of roots and root hairs. 
By reduction of leaf surface. 
d. Influenced not only by the amount of water in 
the soil, but humidity of the air, drying ef- 
fect of wind, effect of heat and light, chemi- 
cal and physical properties of the soil, beat- 
ing of waves en rocks, force of water in 
streams, etc. 
Rainfall, or Precipitation. 
Sometimes injurious. 
2. eight. 
a. Influence of light in photosynthesis. 
b. Influence of light in growth of stem and position. 
c. Influence of light in formation of chorophyll. 
d. Many plants adapt themselves to certain degrees 
of ‘light. 
e. Majority of plants require abundance of light, 
but the amount must be varied according to 
the amount of moisture. 
f. Shade plants have thinner and softer leaves than 
those receiving direct sunlight. 
eee leat 
a. Arctic and alpine plants vegetate at low tem- 
perature. 
Ex., certain algae, fungi, etc. 
b. Annuals require longer summer season. than 
perennials. 
c. Very high temperature injurious. . 
ZS 
