242 



PRACTICAL BOTANY. 



same way. Fill a third tube with water and starch after 

 boiling. Fill a fourth tube with boiled starch and water, 

 to which a small amount of diastase 

 of malt has been added. After some 

 time observe whether water has entered 

 the thistle tubes by osmosis through 

 the diaphragm, and risen in their stems. 

 Test a little of the original solution 

 for sugar. Test the water in the first 

 beaker for sugar. Has sugar passed 

 through the bladder into the water? 

 Also taste the water. 



Test a little of the original starch 

 solution with iodine solution, after di- 



FIG. 166. Apparatus . 



for the study of os- luting with ten times the volume of 

 mosis. (After Mill- water> The characteristic blue color 



is obtained. Test the water in the 

 beaker for starch. Do you find it? Test the water in 

 the second, third, and fourth beakers for starch in the 

 same way. Has starch passed through the bladder into 

 the water? Test the water in these three beakers for 

 sugar. Do you find it in any case ? What is your con- 

 clusion from these tests ? 



The experiment may be varied by using, instead of the 

 thistle tubes, short pieces of glass tubing with the ends 

 covered with bladder. 

 Each piece of tubing so 

 arranged represents very 



wall Q Wlanf nail i 

 Well a plant cell im- 



mersed in water. 



FIG. 167. Imitation plant cell for the 

 study of osmosis. (After Oels.) 



Substances that will pass through membranes by osmosis 

 are called crystalloids; substances that will not so pass 

 are called colloids. 



22. Prove that some diastatic ferment is present in 

 germinating seeds. Germinate some Barley until it is 



