132 ECOLOGICAL RELATIONS 



A little later we learned that rainfall was fnlly as important 

 as a climatic factor as temperature and that it had fully as 

 much influence on the character of the vegetation. Probably the 

 greatest rainfall in the United States is over a small area of 

 Gulf coast extending from w^estern Florida to a short distance 

 west of Xew Orleans, a section of the country well adapted to 

 growing rice and sugar cane. The rainfall of most of the 

 southern states is somewhat higher than for the states north of 

 the Ohio River, but cotton has reached its northern boundary far 

 south of the river. The rainfall of the Rocky Mountain Plateau 

 is lower than for any other part of the United States, giving 

 us a great area of country frequently referred to as the American 

 desert. 



EXERCISES ON PLANT RELATIONS TO SURROUNDINGS 



1. Moisture and Germination. — -Fill two small flower pots with 

 soil of tlie same kind, put into an oven until thoroughly dry, allow to 

 cool, plant seeds in botli, add a definite amount of water to one from time 

 to time, keep the other dry, and keep both in a warm, well-lighted place. 

 Note the germination and growth. 



2. Growth in DifTerent Soils. — Fill several small flower pots with 

 different kinds of soils and sand, plant with seeds of the same kind, give 

 the same amount of water to each at definite intervals, keep in a warm, 

 well-liglitod place. Note time of germination and rate of growth. 



o. Influence of Sand on Rate of Growth.— Take a supply of rich, 

 loamy soil and a supply of clean sand, fill one flower pot with the soil, 

 a second with three parts soil plus one part sand, a third witli two parts 

 soil and tAvo parts sand, a fourth with one part soil plus three parts 

 sand and a fifth with pure sand. Plant the same kind of seeds in all, 

 give the same amount of water from time to time, and keep in a warm, 

 well-lighted placp. Note the time of germination and rate of growth. 



4. Temperature Affects Growth.— Fill two pots with the same kind 

 of good, rich soil and plant with same kind of seeds. Give the same 

 amount of water and keep each in a well-liglitod place, but keep one in 

 a warm place (70 degrees F. or more) and the other in a cold place 

 (af)out 40 degrees F. or less). Note tlie rate of growth. 



5. Effect of Light on Germination and Growth.— Fill two flower 

 pots witli the s;inu- kind of good, ricli soil, i)huit with the same kind of 



