- 80 BOTANY 
have an undue proportion of humus, and exist on the 
sites of old swamps where raupo has, for centuries, 
erown up, died, and decomposed. 
~ Root-acid——From the very nature of the root hair 
it is clear that the food of the plant can pass into it 
only when in solution. Now, though many of the soil 
minerals are, to a slight extent, soluble in water, there 
are others that require an acid to bring them into 
solution. This acid is supplied by the root hairs them- 
selves. Allow the roots of the bean seedling to grow 
over damp blue litmus paper. This, by becoming red 
at the points of contact, shows that an acid is exuded. 
Often the red colour will appear shortly after contact. 
Dissolve gelatine in a white saucer of hot water (ten 
erams of gelatine to 50 e«.c. of water), add litmus 
solution, and then drop in limewater till the solution is 
blue. Just before the gelatine sets, place in it the roots 
of strongly-growing bean seedlings. When the material 
is cold these will be held firmly in position. The change 
of colour from blue to red in the neighbourhood of the 
roots affords a striking and beautiful proof that acid 
is being excreted. ' 
Place on the surface of a piece of highly polished 
marble a number of mustard seeds, cover with damp 
sawdust and keep them damp for about a week. Now 
wash the marble, dry, and rub on it some vermilion. 
When the powder is brushed off, the areas where the 
root acid has eaten in will at once appear. To identify 
this acid, hang a strongly growing bean seedling with 
its roots in a bottle full of limewater, taking care that 
the cork is so fixed that very little air can come into 
contact with the liquid. The limewater becomes milky, 
showing that carbon dioxide is present. New-the-onty 
acid_that-contains-earbon-dioxide_is_carbonic_acid,and 
hence—it—may—be—assumed—that—the_root—gives—ont 
carbonie-aeid.— This is-a-compound_of_carbon dioxide 
FE Cen ee grbon-dioxis e-is formed in 
< yng asyracer 3 lhal tre goeut of Fie 
The fad bhel COz' ty, Suter x fees 
