22 



GROWTH 



plasm), and because plants evaporate large quantities of water 

 from their broad expanse of leaves. A date palm may lose in this 

 way from 100 to 190 gallons of water in a day and an ordinary 

 corn crop absorbs through its roots and loses through its leaves 

 in the course of its growth enough water to cover the ground 

 on which it grows to a depth of seven inches. The result is that 



the effective water supply — 

 difference between water ab- 

 sorbed and water lost — is one 

 of the most important factors 

 in plant growth. 



The absorption of the water 

 results in the development of 

 a pressure in plant cells. This 

 is frequently considerable in 

 amount. In 1874 at Amherst, 

 Col. W. S. Clark surrounded 

 a developing squash with an 

 iron harness provided with a 

 lever attachment and found 

 that the squash, which weighed 

 forty-seven and one-half 

 pounds at the end of the ex- 

 periment, raised a weight of 

 five thousand pounds. The 

 experiment attracted consider- 

 able attention at the time and 

 one highly respected minister of the gospel advised his con- 

 gregation, "If God in his providence has given such enor- 

 mous power to a squash to overcome difficulties, how much 

 more will He give you the power to overcome the difficul- 

 ties that may be in the way of your reaching the true end of 

 living." 



Temperature is another important factor for plant growth 

 and for the growth of cold-blooded animals. It is not so im- 



Figure 12. A dwarf and normal variety of 

 corn grown side by side. After Kempton. 

 Courtesy of the Journal of Agricultural 

 Research. 



