THE WORK OF ROOTS 



143 



caulicles, about an inch long, and thrust the caulicles 

 horizontally into the gelatine so that they are covered 

 by it; arrange several seeds in a saucer in this man- 

 ner, and then cover it with a piece of glass. If car- 

 bonic (or other acid) is being given off by the root, we 

 shall be able to detect it by the change in color (from 

 blue to reddish) of the gelatine around it. The result 

 will be most apparent if the color of the gelatine is 

 as pronounced as possible without being strong enough 

 to make it opaque. mssmBmms ^^^ a ^^ a ^, 



A still better method is to stop- 

 per the neck of a small glass fun- 

 nel at the lower end with a small 

 cork, and then pour in the gela- 

 tine until the neck is completely 

 filled. A Pea with a straight caul- 

 icle may then be placed in the fun- 

 nel with the caulicle directed down- 

 ward into the neck and submerged 

 in the gelatine. The funnel should 

 then be covered with a piece of 

 glass, to retain moisture (Fig. 97), 

 and may be conveniently supported 

 in the manner shown in the figure. 



A simpler method is to use ordinary blue litmus 

 paper, folded as for -filtering and placed in a funnel, 

 which is then filled with earth 1 in which seeds are 



1 The action of the soil on litmus paper must be tested, since sour soils 

 will redden it. 



97. Apparatus to determine 

 whether the root excretes 

 acid; the root is growing 

 in gelatine which has been 

 colored blue by the addi- 

 tion of litmus. 



