As mentioned above, my own experience has led me to accept the first view. Therefore I shall have to show that mutations do yield new and constant forms, while fluctuations are not adequate to do so. Retrograde varieties and elementary species may both be seen to be produced by sudden mutations. Varieties have often been observed to appear at once and quite unexpectedly in horticulture and agriculture, and a survey of these historical facts will be the subject of one of my lectures. In some instances I have succeeded in repeating these observations in my garden under the strict conditions of a scientific experiment, and these instances teach us the real nature of the process of mutation in all its visible features. New elementary [17] species are far more rare, but I have discovered in the great evening-primrose, or _Oenothera lamarckiana_ a strain which is producing them yearly in the wild state as well as in my garden. These observations and pedigree-experiments will be dealt with at due length in subsequent lectures. Having proved the existence and importance of mutations, it remains to inquire how far the improvements may go which are due only to fluctuating variability. As the term indicates, this variability is fluctuating to and fro, oscillating around an average type. It never fails nor does it, under ordinary circumstances, depart far from the fixed average. But the deviation may be enlarged by a choice of extremes. In sowing their seed, the average of the strain is seen to be changed, and in repeating the experiment the change may be considerable. It is not clear, whether theoretically by such an accumulation, deviations might be reached which could not be attained at once in a single sowing. This question is hardly susceptible of an experimental answer, as it would require such an enormous amount of seed from a few mother plants as can scarcely ever be produced. The whole character of the fluctuations shows them to be of an opposite nature, contrasting [18] manifestly with specific and varietal characters. By this method they may be proved to be inadequate ever to make a single step along the great lines of evolution, in regard to progressive as well as to retrograde development. First of all fluctuations are linear, amplifying or lessening the existing qualities, but not really changing their nature. They are not observed to produce anything quite new, and evolution of course, is not restricted to the increase of the already existing peculiarities, but depends chiefly on the continuous addition of new characters to the stock. Fluctuations always oscillate around an average, and if removed from this for some time, they show a tendency to return to it. This tendency, called retrogression, has never been observed to fail, as it should, in order to free the new strain from the links with the average, while new species and new varieties are seen to be quite free from their ancestors and not linked to them by intermediates.