222 BOTANICAL GAZETTE [march 





80 liters of gas. Some leaves fell and others showed epinasty; 

 but the underground parts showed no effect. 



Sambucus canadensis. — Treated 60 days and given 60 liters 

 of gas, the roots were killed. Some roots w r hich were still living 

 showed " tubercles" similar to those upon Populus. The stem 

 below ground was somewhat swollen, due to the development of 



spongy white tissue in the lenticels. 



Ulmus americana. — Treated 9c days and given 180 liters of 

 gas, after 3 weeks the bark cracked vertically just above the sur- 

 face of the ground. After 6 weeks, 2 small limbs died and were 

 removed. About half the leaves fell during the treatment. Near 



■ 



the close of the treatment the underground parts were dead and 



cracks extended throughout the bark and cortical tissue. There 



was a small amount of proliferation tissue just outside the vascular 



system. 



Practical suggestions for florists 



To detect illuminating gas in a greenhouse, the florist should 

 provide himself with some vigorous plants of one of the following: 

 tomato, castor bean, scarlet sage, Jimson weed, or sensitive plant. 

 These should be grown in pots so that they may readily be handled, 

 and should have from 6 to 1 2 or more leaves. They must also be 

 in vigorous condition; otherwise they may not respond should 

 illuminating gas be present. These should be placed at various 

 locations throughout the greenhouse and left 24-48 hours with 

 poor ventilation. All the plants named will respond to traces of 

 illuminating gas within this period at ordinary temperatures-. 



With only a trace of gas present in the air, the epinastic 

 response of the leaves will be very noticeable if these plants are 

 compared with normal plants without gas. This bending down 

 of the leaves will increase with the concentration of the gas present 

 in the air. All these plants will drop their leaves with a concen- 

 tration below the limit of the odor of gas. The older leaves fall 

 first, the younger leaves being retained until there is 1 part of 

 illuminating gas to 1000 of air. 



Summary 



1. The following plants are admirably adapted for use as test 

 plants for illuminating gas in greenhouses: Lycopersicum escu- 





