MINUTE STRUCTURE OF LEAVES. 121 
starch from water and carbonic acid gas. Parasites, like the 
dodder, which are destitute of green coloring-matter, cannot 
do this, neither can saprophytes or plants which live on 
decaying or fermenting organic matter, animal or vegetable. 
Most saprophytes, like the moulds, toadstools, and yeast, are 
flowerless plants of low organization, but there are a few such 
as the familiar Indian pipe, Fig. 100, which flourish on rotten 
wood or among decaying leaves, that bear flowers and seeds. 
152. Detection of Starch in Leaves. — Starch may be found 
in abundance by microscopical examination of the green parts 
of growing leaves, or its presence 
may be shown by testing the 
whole leaf with iodine solution. 
153. Experiment 29. Occur- 
rence of Starch in Nasturtium Leaves. 
— Boil some bean leaves or leaves of 
nasturtium (Tropwolum) in water for 
a few minutes to kill the protoplasmic 
contents of the cells and to soften and 
Pe teh: grains, FIG 101 —Leaf of Tropzolum 
Soak the leaves (after boiling) in partly covered with Disks of Cork 
strong alcohol for a day or two to and exposed to Sunlight. 
dissolve out the chlorophyll, which 
would otherwise make it difficult to see the biue color of the starch test, 
if any were obtained. Rinse out the alcohol with plenty of water and then 
place the leaves for half an hour in a solution of iodine, rinse off with water 
and note what portions of the leaf, if any, show the presence of starch. 
154. Experiment 30. Consumption of Starch in Nasturtium 
Leaves. —Sélect some healthy leaves of Tropzolum on a plant growing 
vigorously indoors or, still better, in the open air. Shut off the sunlight 
from parts of the selected leaves (which are to be left on the plant and as 
little injured as may be) by pinning circular disks of cork on opposite 
sides of the leaf, as shown in Fig. 101. On the afternoon of the next 
day remove these leaves from the plant and treat as described in the pre- 
ceding experiment, taking especial pains to get rid of all the chlorophyll 
by changing the alcohol as many times as may be necessary. What does 
this experiment show in regard to the consumption of starch in the leaf ? 
What has caused its disappearance ? 
