7 8 PLANT PHYSIOLOGY. 



or other leafy plant, and a glass jar just large enough to hold the 

 pot ; cut a small hole in the center of a piece of rubber cloth which 

 is somewhat larger than needful to cover the top of the jar; slip the 

 rubber up over the pot and tie to the stem by a stretched rubber 

 band, and fasten the cloth over the top of the jar by a tight wire (see 

 Fig. 14, plant in the center.) Insert a short thistle-tube through a 

 tiny hole. Make sure that the pot is enclosed water-tight. Weigh 

 on the spring-balance three times daily, as near sunrise as possible, 

 at midday, and at sunset, and water once daily through the thistle- 

 tube with an amount about equal to that given off. Keep a record 

 of temperature, moisture, and sunshine, and plot all four records 

 together. 



FIG. 14. PREPARATION OF PLANTS FUR STUDY OF TRANSPIRATION. 



( )ne -fourth the true size. 



(In using the spring-balance, the weight must always be placed ex- 

 actly in the center?) 



Another method of preventing evaporation from the pot is to wrap it 

 completely in rubber cloth, gathered up and tied about the stem of the 

 plant as shown in Fig. 14 on the left. The use of the glass, however, 

 has three advantages : it allows the condition of the soil to be seen, thus 



