CONTROLLING PLANT MOISTURE. 39 



gatlons are designed to formulate simple equations of measur- 

 able factors, from which the origination, somatic response, 

 physiological action, trajectory in evolutionary change, and 

 distributional movements of living forms may be adequately 

 considered and advanced interpretations of these major activi- 

 ties of living forms made possible. 

 Desert Laboratory. 



A METHOD FOR CONTROLLING PLANT 



MOISTURE. 



The method here described was developed for main- 

 taining constant moisture conditions in the soil of pots, boxes 

 or other containers in which plants are grown. It is useful 

 in all cases where plants are to be grown without daily atten- 

 tion to watering, and is the only method I have discovered 

 which avoids the puddling of the surface soil and the great 

 fluctuations in general water content incident to periodical 

 watering. 



A porous clay cup* of the form used in evaporation 

 measurement (as described in Publication No. 50 of the Car- 

 negie Institution and in the Plant World for December, 

 1907) is filled with water and stoppered with a perforated 

 rubber stopper bearing a tube of glass and rubber or of lead, 

 which connects with a reservoir of water. The tube must be 

 filled with water when the stopper is inserted, so as to avoid 

 any air bubbles between the reservoir and the cup. The res- 

 ervoir may be a large bottle or any suitable container. A 

 convenient length of tube is about a meter, although this is 

 varied according to conditions. The cup is buried in the soil 

 of the pot or box in which the plants are to be grown. In 

 the case of a pot it is convenient to place it erect in the center, 

 when a larger vessel contains the soil the cup may be placed 

 horizontally and at a depth of five to twenty centimeters. 



* The porous clay cups here used may be obtained by addressing Dr. Forrest Shreve, 

 John Hopkins University, Baltimore, Md. 



