Page:Popular Science Monthly Volume 83.djvu/242

238 mechanically restrained by the use of plaster-of-Paris casts, and from 2 to 6 atmospheres for the radial pressure of roots. The geotropically sensitive nodes of the wheat stem gave a pressure equal to 15 atmospheres when mechanically restricted. The maximum osmotic pressure m these cases would be obtained by a solution of potassium nitrate equal to about 5 per cent.

Colonel W. S. Clark's experiment with the lifting power of a squash, made in 1874 at Amherst, was one of the first attempts to learn the growing power of plants. This experiment attracted quite a little

attention at the time. One highly respected minister of the gospel had a drawing of the harnessed squash distributed among his congregation in tract form to illustrate the great moral principle that "If God in his providence has given such enormous power to growing vegetation to overcome difficulties, how much more will he give to you power to overcome the difficulties that may be in the way of your reaching the true end of all living."

This experiment was carried on in a greenhouse under the most favorable conditions, and by arranging an iron harness provided with a lever attachment the squash was found to raise 5,000 pounds. The squash was horticulturally known as the Mammoth Yellow Chile variety, and at the close of the experiment weighed 47 pounds. It is estimated that the squash developed over 80,000 feet, or about 15 miles of roots, an average of about 1,000 feet daily. From the data given in this experiment we have been able to estimate roughly the osmotic pressure of the cells, which might be supposed to be most active.