1905] BRIEFER ARTICLES 149 
preferably cut slightly larger than the chamber-rings so they will cling 
half-way up the latter) be placed in the chambers, which are then applied 
to the leaf, the change of color in transpiration may be observed with the 
greatest clearness and facility. Incidentally, the tightness of the chambers 
(when not on the leaf) permits the papers to retain their dryness and red 
color for a considerable time, so that there is no need of haste in applying 
them to the plant. The second accessory ring is broken, and is intended 
to hold tinfoil or any fabric tightly to the chamber-ring. Thus if projecting 
FiG. 3. 
veins prevent a connection of chamber withleaf "sufficiently tight for 
Some special purposes, a band of thin rubber may be held by the broken 
ring in such a way that it will project against the leaf, filling the spaces 
between the veins. But there is a more important use for the broken 
ting, which is to attach tinfoil patterns or screens to the chamber-rings 
for the demonstration of the necessity of light in photosynthesis. The 
common method of demonstrating this important physiological fact by 
vias of corks or other material attached to both faces of a leaf is fallacious 
(since the absence of starch thus shown is due as much to absence of 
carbon dioxid as to absence of light), and a logical proof involves use of 
