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SOME SIMPLE PHYSIOLOGICAL APPARATUS 



By George E. Stone 



The writer has for many years conducted a physiological prac- 

 ticum connected with botanical teaching, and as might be ex- 

 pected in any course requiring experiments, many methods and 

 devices have been incidentally developed, some of which have 

 proved fairly satisfactory in demonstrating certain principles, and 

 others may find them suggestive in their lines of work. 



Method of Demonstrating Difference in Transpiration 

 Between Upper and Lower Sides of the Leaf 



For demonstrating the difference in transpiration between the 

 upper and lower sides of the leaves we have used the apparatus 

 shown in figures i and 2, which illustrate a calla plant with the ap- 

 paratus in place. It consists of two simple hygrometers 5 cm. in 

 diameter, similar to those often used in cigar cases. These are 

 attached to two pieces of metal tubing slightly larger in diameter 

 than the hygrometers, each tube being about 4.5 cm. long. The 

 hygrometers are placed in the end of each tube by means of 

 rubber sheeting cut so as to fit tightly around the hygrometers. 

 The rubber is then turned over the end of the metal and tied on 

 with a thread. The tubes containing the hygrometers are placed 

 on either side of the leaf, the ends of the tubes being supplied 

 with rubber rings or bands so that the two halves of the metal 

 cylinder, each containing the hygrometer, can be pressed against 

 the leaf firmly but without injuring it. Glass tubes or even large 

 corks may be substituted for metal if the proper size is obtain- 

 able. By taking readings of both hygrometers at the beginning 

 of the experiment and at different times afterwards the relative 

 difference in the transpiration between the upper and lower sides 

 of the leaf is fairly accurately determined. 



Method of Demonstrating the Effects of Various 

 Factors on Transpiration 

 There are many simple experiments which may be done to 

 illustrate the effects of various factors on transpiration. In our 



