154 COLLEGE BOTANY 



fruit of a watermelon will likewise contain more water than 

 the seeds or the stems and leaves. These and many other illus- 

 trations that might be given lead us to believe that there must 

 be some very complex structural and physiological factors which 

 influence and control the amount of the water contained in the 

 different parts of the plant. Furthermore, it is very evident that 

 water is a very important factor in the living cell. We fully 

 appreciate that water is absolutely necessary -for life, growth 

 and reproduction, but we do not fully understand the significance 

 of water in the living plant. 



Necessity cf Water. Water is necessary for all the life 

 functions of the plant. Therefore, the water supply and its 

 distribution throughout the year determines in great measure 

 the kinds and number of plants found in different localities. In 

 fact, water is one of the most important environmental factors 

 in plant growth, and plant distribution over the earth. A study 

 of the distribution of plants over the earth will show that water 

 is fully as important as, possibly more important than, tempera- 

 ture and soil qualities. The great movements of the human race 

 have been far more dependent on water for the production of 

 their food and other 1 necessities of life, for use in their vari- 

 ous manufacturing industries and for transportation than on 

 any other factor. The movements of mankind throughout all 

 time have depended primarily on the amount and distribution of 

 water. This is especially noticeable in a study of the settle- 

 ment of America. The lines of migration have been primarily 

 along the waterways and the success of settlements has been de- 

 pendent more on water than on any other natural factor. Many 

 thousands of acres of excellent land in our great West are not 

 and cannot be used because of the lack of water. 



