MINUTE STKTJCTURB OP 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. 



ISS. Experiment 29. Occur- 

 rence of Starch in Nasturtium Leaves. 

 — Boil some bean leaves or leaves of 

 nasturtium f Tropxolum) in water for 

 a few minutes to kill the protoplasmic 

 contents of the cells and to soften and 

 swell the starch-grains. 



Soak the leaves (after boiling) in 

 strong alcohol for a day or two to 

 dissolve out the chlorophyll, which 

 would otherwise make it difficult to see the blue color of tha 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. — Select some he?,lthy leaves of Tropseolum 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 ? 



Fig. 101^ — Leaf of Tropseolum 

 partly covered with Bisks of Corlc 

 and exposed to Sunlight. 



