ILLUSTRATIVE STUDIES 1 55 



XVI) on the slide against the coverglass and as the reagent dif- 

 fuses under watch its progressive reaction on the chloroplasts. 

 Is starch demonstrated? In precisely what part of the cell 

 did it occur? Measure one of the starch grains. Draw a 

 single cell as seen before and after application of chloral hydrate. 



2. Study Spirogyra in the same manner and draw a single 

 cell as before. 



3. Make free-hand cross sections of some leaf and mount 

 the thinnest — even the smallest fragments — in a drop of water. 

 Find the palisade and spongy parenchyma. Do the chloro- 

 plasts have the same position in the cells as those of the moss 

 leaf were found to have? Treat with chloral hydrate-iodine 

 as above and watch for the first indications of starch. Do 

 you find evidence that the starch was formed by the chloroplasts ? 

 How large are these bits of food that have just been compounded 

 from CO2 and water? Draw a portion of the section from one 

 surface to the other as seen before and after the chloral hydrate 

 reaction. 



4. Study in the same way leaves from plants that have been 

 kept in the dark for forty-eight hours, and leaves from plants 

 that have been kept all day in strong diffuse light but in an 

 atmosphere from which CO, has been absorbed. To do this 

 set a potted plant on a glass plate; put a stick of KOH in a bottle 

 beside it; place a tubulated bell-jar over all and seal it with 

 sealing wax to the glass plate; stop the opening in the bell-jar 

 with a perforated cork, and insert through the cork a glass tube 

 bent at right angles, and into the horizontal arm of this place 

 loosely small lumps of soda lime. Now air can enter but the 

 CO2 will be absorbed from it by the soda lime, and that CO2 

 evolved by the respiration of the plant will be absorbed by the 

 KOH under the bell-jar. 



Arrange a check experiment in all respects like this one ex- 

 cept that sawdust is to take the place of the soda lime and the 

 KOH under the bell-jar is to be omitted. It will not do to place 

 these plants in direct sunlight because the air in the bell-jar 

 would become too hot. The plants used in this experiment 



