1904] BENNETT: ARE ROOTS AEROTROPIC 247 
Finally, to increase the difference in the oxygen pressure on 
opposite sides of the roots as much as possible, the water in which 
the roots were supported opposite a chamber of air was prevented, 
by the device illustrated in fig. 2, from replenishing its supply of 
oxygen which was exhausted through respiration. A small 
aquarium was chosen which was hermetically sealed by weight- 
ing down a glass cover (/) on a cushion of rubber (Z) cemented 
securely to the upper edges of the aquarium. The chamber (2) 
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Fic, 2.—A, aquarium; &, chamber containing gas; C, seedlings; D, height of 
water; £, rubber cushion; F, glass cover; /, aperture in cover; 7, rubber stopper; 
4, glass tube through which gas enters; Z, glass tube for escape of water; S, weights; 
a, rubber tubing. 
containing air was a rectanglar glass dish, 14% by 8 by 4™, 
Supported, at angles between 20 and 45° to the horizontal, by 
pressing in small pieces of rubber tubing (a) between the ends of 
the dish and the sides of the aquarium. No membrane was used 
to inclose the gas. When the required seedlings (C), which had 
been growing in a vertical position in a damp chamber from 12 
to 24 hours, were supported before the air chamber so that their 
tips extended 1 to 3™" below the upper edge of the chamber 
and 1 to 5™" away from it, the aquarium, already partly filled, 
was now completely filled with water, the cover pressed down, 
and the water above the roots replaced through tube Z by gas 
