Four sugars having the formula C6H12O6, namely, glucose, fructose, mannose, and galactose, occur very commonly and widely distributed in plants. In addition to these, thirteen others having the same percentage composition have been artificially prepared, while seven additional forms are theoretically possible. In other words, twenty-four different compounds, all having the same empirical formula and similar sugar-like properties are theoretically possible. In order to arrive at a conception of this multiplicity of isomeric forms, it is necessary to understand the two types of isomerism which are involved. One of these is structural isomerism, and the other is space- or stereo-isomerism.
While color of flowers seems as though it were attraction enough, it is very likely that their fragrance or perfume is still more seductive in its power of luring insect visitors and repelling useless ones. Poets have called this perfume the soul of the flower, and in its almost intangible beauty it might well be so called were it not for the fact that it appears to be of not the slightest use, except as a lure. In all the equipment of seduction there is none like this fragrance of flowers for attracting insects.