The whole vegetable kingdom exhibits a constant struggle between progression and retrogression. Of course, the great lines of the general pedigree are due to progression, many single steps in this direction leading together to the great superiority of the flowering plants over their cryptogamous ancestors. But progression is nearly always accompanied by retrogression in the principal lines of evolution, [15] as well as in the collateral branches of the genealogical tree. Sometimes it prevails, and the monocotyledons are obviously a reduced branch of the primitive dicotyledons. In orchids and aroids, in grasses and sedges, reduction plays a most important part, leaving its traces on the flowers as well as on the embryo of the seed. Many instances could be given to prove that progression and retrogression are the two main principles of evolution at large. Hence the conclusion, that our analysis must dissect the complicated phenomena of evolution so far as to show the separate functions of these two contrasting principles. Hundreds of steps were needed to evolve the family of the orchids, but the experimenter must take the single steps for the object of his inquiry. He finds that some are progressive and others retrogressive and so his investigation falls under two heads, the origin of progressive characters, and the subsequent loss of the same. Progressive steps are the marks of elementary species, while retrograde varieties are distinguished by apparent losses. They have equal claim to our interest and our study. As already stated I propose to deal first with the elementary species and afterwards with the retrograde varieties. I shall try to depict them to you in the first place as they are seen in [16] nature and in culture, leaving the question of their origin to a subsequent experimental treatment. The question of the experimental origin of new species and varieties has to be taken up from two widely separated starting points. This may be inferred from what we have already seen concerning the two opposing theories, derived and isolated from Darwin's original broad conception. One of them considers mutations as the origin of new forms, while the other assumes fluctuations to be the source of all evolution.