The Prevalence of Green Color in Plants 23 



are discernible, but a very different story is told by the micro- 

 scope. That indispensable instrument shows in the lighted leaves 

 the presence of tiny white grains (figure D, Plate I), which are 

 absent from the leaves that were darkened, while chemical tests 

 prove these grains to consist of a definite and familiar chemical 

 substance, starch. 



This fact that starch makes appearance in ordinary green 

 leaves when exposed to the light but not in those kept in the dark, 

 is so important in plant physiology that the reader should make 

 some further and practical acquaintance with the matter. If he 

 selects some one of the commoner house plants, (e. g., Fuchsia, 

 Garden Nasturtium, Horseshoe Geranium), covers some of the 

 leaves from the light by a box, exposes the plant for a day or 

 two to light, removes the darkened and lighted leaves at the 

 close of the second day, dips them for a moment into boiling water, 

 blanches them of chlorophyll, by aid of warm alcohol, immerses 

 them in water a minute to neutralize the brittleness the alcohol 

 causes, spreads them out in a white saucer, and covers them with 

 a solution of iodine diluted from the tincture he may buy from 

 a druggist, he will be rewarded by seeing a very remarkable 

 difference develop between the lighted and darkened leaves, for 

 immediately the former will all turn a very dark blue, while the 

 latter will remain of their natural cream color. Now iodine, as 

 anyone may prove by a touch to some part of his starched linen, 

 though brown of itself turns starch a dark blue; and thus our 

 experiment proves that the leaves form starch in the light but 

 not in the dark. So exact, indeed, is this relation that if a famil- 

 iar sharp pattern be cut in opaque material and applied during 

 the experiment to the upper face of a leaf, that pattern is found 

 reproduced in equivalent sharpness when the iodine test is ap- 

 plied; and not only this, but if a photographic negative be used 

 instead of the pattern, the picture will be printed very accurately 

 in starch in the leaf, and may be " developed" in remarkable 

 fashion by the addition of iodine. For full success in these two 



