1915] HARVEY &■ ROSE— ILLUMINATING GAS 31 



representing iS families. Controls were maintained throughout. 

 The seeds were allowed to germinate and grow for periods of 25-60 

 days. 



B. THE EFFECT OF ILLUMINATING GAS ON ROOTS WITH NO SOIL 

 PRESENT 



i. With roots alone exposed to gas 



In order to expose the roots without exposing the shoots, the 

 following method was employed. Moist-air chambers were made 

 from Sditer, wide-mouthed bottles; 6-8 short glass tubes were 

 inserted in the corks of each of these bottles so that the tap roots 

 of young seedlings of Vicia Faba could be admitted to the chamber. 

 The space between a root and the sides of a tube was sealed by 

 means of a short length of pure gum tubing which had been previ- 

 ously fitted to the outer end of the glass tube. Definite amounts 

 of illuminating gas or ethylene were admitted through a small 

 glass tube reaching to the bottom of the bottle. The pressure 

 resulting from the addition of the small volume of gas was relieved 

 through a second short tube. 



2. With entire plant exposed to gas 



Seeds of tomato, radish, and mustard were allowed to germinate, 

 and when the hypocotyls had reached a length of o. 5 cm. they were 

 transferred to flower pots under bell jars provided with water seals. 

 The seedlings were fixed to the rims outside of the flower pots, so 

 that the roots in growing would hang free in the air. Definite 

 amounts of illuminating gas could be easily added. 



C. EFFECT OF ILLUMINATING GAS ON ROOTS GROWING IN SOIL 

 MEDIUM 



i. Quantitative tests 



In these tests young seedlings (two or three months old) of 

 Catalpa speciosa, Ailanthus glandulosa, and Glcditsehia triacanthos 

 were used. A few days before the beginning of the experiments, 

 the seedlings were transplanted from the pots, in which they had 

 germinated, to large battery jars filled with coarse quartz sand. 

 Two glass tubes for admitting gas were thrust into the sand and 



