TRANSPIRATION. 83 



the relative transpiration as measured by the water collecting inside 

 the glasses. (The glasses may be scaled to ttie leaf by use of soft wii.v, 

 Ptfgt' ^.o, but it is not necessary.} 



Another very excellent way of testing this is through use of Stahl's 

 cobalt chloride method. If slips of filter-paper be dipped in a 4 to 5^ solu- 

 tion of cobalt chloride and then dried over a flame, they will be blue in 

 color, but will turn red on access of any moisture, the more quickly the 

 greater the moisture. Pieces of the paper put in the two watch-crystals 

 used above give good results, or they may be simply placed against the 

 leaf surfaces and covered from the moisture of the air with bits of mica, 

 held in place by clamps. The method is used by Stahl to determine 

 whether stomata in given leaves are open or closed. There are other 

 excellent methods of testing this by use of calcium chloride, an eager 

 absorbent of water, which is weighed (Detmer, page 215); by use of 

 hygroscopic awns (Darwin and Acton, 103) ; and by other methods de- 

 scribed in the works on the subject. (See Note 6 of the Addenda.) 



45. Is water ever given off by the aerial parts of plants in other 

 form than vapor ? 



Answer by Experiment 23. 



EXPERIMENT 23. Of course the liquid form is the only other 

 ordinarily possible. To test whether liquid water is thus given off, 

 a vigorous young plant of high transpiring power should be selected 

 when in full transpiration (and conduction), and the transpiration 

 checked. This may be done in various ways, but most conveniently 

 by darkening the plant and surrounding it with a saturated atmos- 

 phere. Select young plants of Tropseolum, grasses (preferably seed- 

 lings), corn, or others, cover with a bell-jar and place for one or two 

 hours in a warm dark place. 



How may the result be interpreted ? 



46. Construct a diagram (based upon all of your sources of 

 information) showing in the simplest possible way the path of 

 the water from the soil to the air through the plant. Indicate 

 the known and supposed physical forces at work at the different 

 points. 



47. What ecological results and aspects of Transpiration can 

 you think of? 



Answer from your own observation, and from other avail- 

 able sources. 



48. Prepare a synoptical essay, of not over 500 words, upon 

 Absorption, Transfer, and Transpiration in Plants. 



