170 



FOUNDATIONS OF BOTANY 



EXPERIMENT XXXV 



Occurrence of Starch in Nasturtium Leaves. — Toward the close of 

 a very sunny day collect some bean leaves or leaves of nasturtium 

 (^Tropteolum). ■ Boil these 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 diffi- 

 cult to see the blue color of the starch test, if any were obtained. 

 Rinse out the alcohol with plenty of water 

 and then place the leaves for ten or fifteen 

 minutes in a solution of iodine, rinse off 

 with water and note what portions of the 

 leaf, if any, show the presence of starch. 



EXPERIMENT XXXVI 



Consumption of Starch in Nasturtium 

 (Tropoeolum) Leaves. — Select some healthy 

 leaves of Tropseolum on a plant growing 

 vigorously indoors or, still better, in the 

 open air. Shut ofE the sunlight from 

 parts of. the selected leaves (which are to 

 be left on the plant and as little injured 

 as m^ay be) by pinning circular disks of cork on opposite sides of 

 the leaf, as shown in Fig. 123. On the afternoon of the next day 

 remove these leaves from the plant and treat as described in the 

 preceding experiment, taking especial pains to get rid of all the 

 chlorophyll by changing the alcohol as manj; times as may be neces- 

 sary. What does this experiment show in regard to the consump- 

 tion of starch in the leaf? What has caused its disappearance? 



182. Rate at which Starch is manufactured. — The 

 amount of starch made in a day by any given area of 



1 The leaves, collected as above described, may, after boiling, be kept in 

 alcohol for winter use. They also make excellent material for the micro- 

 scopical study of starch in the leaf. 



Fig. 123. — Leaf of Tropseo- 

 lum partly coyered -with 

 Disks of Cork and ex- 

 posed to Sunlight. 



