124 SOUTH AFRICAN BOTANY 
87. Experiment 1.—T'o see which elements are neces- 
sary for healthy growth. 
Apparatus.—Large glass jars, holding one litre, with 
corks to fit, black or brown paper, slips of Tradescantia 
or Pea seedlings, or Mealie seedlings (Tradescantia 
gives the best results), distilled waters, various salts. 
Method.—Measure out a litre of distilled water, and 
weigh out one gramme of potassium nitrate, gramme 
each of sodium chloride, calcium sulphate, magnesium 
sulphate and calcium phosphate. ‘Thoroughly clean the 
jars, and rinse with distilled water, then dissolve the 
above salts in the litre of distilled water and fill the jar 
with it. Add a few drops of iron chloride solution. 
This is the Normal Solution, and contains all the essen- 
tial elements except carbon. Cut a slip of Tradescantia 
(Wandering Jew) just below a node, fix 14 through a slit 
in the cork, and fix the cork in the bottle. There must 
be an air space between the cork and the bottle, and the 
cork must be perfectly dry. Then cover the jar with black 
or brown paper, and label it. Make up the solutions 
for the other jars in the same way, but in each one 
omit one element, e.g. in one use sodium nitrate, instead 
of potassium nitrate, thus omitting potassium ; in another 
use potassium phosphate or sulphate, instead of the ni- 
trate, thus omitting nitrogen. Choose slips of Trades- 
cantia as nearly as possible the same size as the first, and 
fix onein each bottle. Label each bottle, saying what ele- 
ment is omitted ; one bottle should contain distilled water 
only, and one should have everything except the iron 
chloride. Unless the corks are kept perfectly dry, the 
plants are apt to be attacked by mould ; butif the experi- 
