238 PRACTICAL BOTANY. 



through which fresh air is admitted deprived, of carbon 

 dioxide. Recall similar experiments performed with Spi- 

 rogyra and other Algae. 



b. Stand cylinders, bearing healthy cultures of seed- 

 lings in Sachs' food solution, in a shallow dish of water. 

 Cover with a tubulated bell jar, so placed that the water 

 in the shallow dish seals the bottom. In the tubulature 

 insert tightly a rubber stopper bearing a bulb tube con- 

 taining caustic soda or caustic potash. Fresh air deprived 

 of carbon dioxide is admitted through the tube. Place 

 the whole in strong sunlight. Examine daily. Does the 

 plant continue to thrive ? More than one half of the solid 

 matter of plants is carbon. Plants thrive and attain their 

 best maturity in Sachs' solution which contains no carbon 

 in any form. They must therefore obtain it from the air. 



17. Show that oxygen is necessary for growing plants. 



a. Fill two ordinary chemical retorts, neck and all, with 

 water that has been boiled to expel the contained gases. 



Put a few Peas or Beans in the bot- 

 tom of each retort, and stand the 

 retorts, neck down, in a vessel of mer- 

 cury. Let them stand twelve hours 

 to soften the seeds. Then run hydro- 

 gen gas into one from an ordinary 

 hydrogen apparatus, and into the other 

 FIG. 163. Tubes for blow ordinary air by means of a bel- 



the study of seed- , ,. . ,-, -, . 



lings when deprived low s> inclining the retojts to dram out 



of oxygen. (After the water. Allow both to stand, and 



observe that the seeds in the retort 



containing h} 7 drogen do not germinate, while those in the 



retort containing air develop. 



b. On the bottom of a 500 c.c. flask place 011 a wet 

 filter paper a layer of Barley that has been soaked in 

 water twelve hours, and stand a test tube containing a 

 strong solution of caustic potash in the flask. Stopper 



