64 PHYSIOLOGY. 



Can it be that this is because the oxygen was driven from 

 the water in boiling? We shall see. Let us take the vessel 

 containing the water, or some other boiled water, and agitate it 

 so that the air will be thoroughly mixed with it. In this way 

 oxvgen is again mixed with the water. Now place the plant 

 again in the water, set in the sunlight, and in several minutes 

 observe the result. No oxygen or but little is given off. There 

 must be then some other requisite for the evolution of the oxvgen 



132. The gases are interchanged in the plants. — We will now 

 introduce carbon dioxide again in the water. This can be done 

 by leading CO, from a gas generator into the water. Broken 

 bits of marble are placed in the generator, acted upon bv h^'dro- 

 chloric acid, and the gas is led o\'er by glass tubing. Now if we 

 place the plant in the water and set the vessel in the sunlight, in 

 a few minutes the oxygen is given off rapidly. 



133. A chemical change of the gas takes place within the 

 plant cell. — This leads us to believe then that COj is in some 

 way necessary for the plant in this [process. Since oxygen is 

 given off while carbon dioxide, a different gas, is necessary, it 

 would seem that a chemical change takes place in the gases 

 within the plant. Since the process takes place in such simple 

 plants as spirogvra as well as in the more bulkv and higher 

 plants, it appears that the changes go on within the cell, in fact 

 within the protoplasm. 



134. Gases as well as water can diffuse through the proto- 

 plasmic membrane.— Carbon dioxide then is aljsorijed l)y the 

 plant while o.xygen is given off. We see therefore that gases as 

 well as water can diffuse through the protoplasmic membrane of 

 plants under certain conditions. 



2. Where Starch is Formed. 



We have found by these simple ex|)eriments that some 

 chemical change takes place within tlie protoplasm of the green 

 cells of plants during the al>sori)lion of carbon tlio.xide and the 

 giving off of oxvgen. We should examine some of tlie green 

 parts of tliose plants used in the experiments, or if they are not 



