1915] HARVEY & ROSE—ILLUMINATING GAS 31 
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representing 18 families. Controls were maintained throughout. 
The seeds were allowed to germinate and grow for periods of 25-60 
ays. 
B. THE EFFECT OF ILLUMINATING GAS ON ROOTS WITH NO SOIL 
RESENT 
1. With roots alone exposed to gas 
In order to expose the roots without exposing the shoots, the 
following method was employed. Mboist-air chambers were made 
from 8-liter, 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 0.5 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 
1. Quantitative tests 
In theSe tests young seedlings (two or three months old) of 
Catalpa speciosa, Ailanthus glandulosa, and Gleditschia 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 
