a. Derived from soiutions of eroded and dissolved 
rock formations. 
b. From decaying animal and piant remains. 
c. From certain gases in rain water, salts of sea 
Wie iene ie 
d. Elements necessary for plant growth. 
Oxygen, hydrogen, carbon, nitrogen, phos- 
phorus, sulphur, iron, potassium, calcium, 
magnesium. , 
These are derived from the air, soil, certain 
compounds brought into solution by the 
plant, etc. 
Certain substances found in solution in the 
soil which are harmful to the plants. 
Modification induced by chemical conditions 
of soil. 
8. Physical or mechanical conditions of the soil. 
Difference of vegetation in rocky places, sandy soil, 
soil rich in humus, clay soils, peat moors, etc. 
g. Physiography. : : 
Mountains, oceans, rivers, etc., present barriers to 
migration, difference in altitude and temperature, 
exposure to light and sun’s heat, and affect 
water content of the soil. 
10. Mechanical adaptations in plants for seed distribution, 
etc: 
2nd, Climatic factors. 
ie denyoseilk 
2, -demperature 
3. Physiography. 
ard, Biotic factors. 
1. Pollination by insects. 
Distribution of seeds by birds and other animals. 
Burrowing animals aid in soil culture. 
Squirrels distribute nuts. 
Man’s agency. 
Protection of plants among themselves. 
Work of parasites, bacteria, etc. 
Power of plant to relate itself to environment. 
COON SoS 
25 
