278 BOTANICAL GAZETTE [APRIL 
which may be either two separate strips covering the compartments and 
therefore the halves of the leaf, or a single sheet 5 7 inches in size. The 
cover may then carry tin-foil, cut with any desired pattern, gummed to its 
under surface; or it may carry vials of pure colors correlative to the light 
and dark spots of the chlorophyll spectrum (as was the case when the 
accompanying photograph was taken); or it may be replaced by a 5X7 
negative for Gardiner’s striking starch-printing experiment. The arrange- 
ment does not of course permit as free access of carbon dioxid as the 
uncovered leaf enjoys, but this is only a matter of degree and does not affect 
the result when sufficient time is allowed for the experiment. In using 
Fic. 2.—Normal light screens. 
this, as any other, light screen it is desirable to expose the plants not to 
direct sunlight but to strong diffused light, which is nearer the optimum 
and has less heating effect. The leaves of course are subsequently blanched 
and treated with iodin in the usual manner. 
The smaller screen, of a less range of usefulness but much cheaper, is 
made upon the same general principle except that it is constructed to clasp 
a portion of a leaf. A spring clip holds a glass disk against the upper 
surface of a leaf, which is supported below by a grating of threads stretched 
across the top of a ventilated dark box. The glass is removable from the 
clip and may carry a tin-foil screen cut with a pattern and gummed to its 
under surface as in the figure; or it may be used to hold a photographic 
