142 EXPElilMENTS WITH PLANTS 



lently).- Place the seedling in the bottle so as to sub- 

 merge the roots, and tuck a little cotton around the 

 stem of the plant where it passes through the cork. 

 Arrange the second bottle in the same way, but put no 

 plant in it; simply fill the notch in the cork with 

 cotton. If, now, the roots give off carbonic acid we 

 shall expect to find the lime-water in which they are 

 submerged turning milky after a time, while that in the 

 control bottle remains clear (or shows a slight degree 

 of milkiness due to the carbonic acid of the air). 



In order to get a better idea of the giving off of 

 acid by the root, we should grow some roots in gela- 

 tine to which litmus has been added. This very inter- 

 esting experiment may be performed in a variety of 

 ways. Some of the so-called "sparkling gelatines" 

 used for cooking are preferable. Dissolve one part 

 of gelatine in about five parts of water. This is most 

 conveniently done by letting it soak in cold water over 

 night and then putting it on a water-bath (see Figs. 51- 

 and 206). When the gelatine is dissolved, add enough 

 litmus dissolved in water ^ to give the gelatine a strong 

 (reddish purple) color. Now add lime-water cau- 

 tiously until the color changes to blue. The gelatine 

 should now be filtered, as described on page 369, and 

 should then be quite clear. Pour some of it into white 

 saucers to the depth of a quarter of an inch; when it 

 has "set," take some Peas (or other seeds, with straight 



1 Obtainable at druggists'. 



