I am not referring here to the few cases in which bacteria were made colourless or non-virulent by outside factors, or in which certain fungi were forced to permanent agamic reproduction by abnormal external conditions and were shown to retain their “acquired properties” after the external conditions had been restored. In these cases only reproduction by simple division occurred, and that does not imply the true problem of inheritance. Nor am I referring to the few cases of non-adaptive “modifications” found by Standfuss and Fischer, in which butterflies that had assumed an abnormal kind of pigmentation under the influence of abnormal temperature acting upon the pupa, were seen to form this same kind of pigmentation in the next generation under normal conditions of temperature. These cases, though important in themselves, are capable perhaps of a rather simple explanation, as in fact has been suggested. Some necessary means both of inheritance and of morphogenesis, the former being present in the propagation cells, may be said to have been changed or destroyed by heat, and therefore, what seems to be inherited after the change of the body only, would actually be the effect of a direct influence of the temperature upon the germ itself.[151] Let me be clearly understood: I do not say that it is so, but it may be so. What seems to me to be more important than everything and to have a direct bearing on the real discovery of the inheritance of acquired characters in the future, is this. In some instances plants which had been forced from without to undergo certain typical morphological adaptations, or at least changes through many generations, though they did not keep the acquired characters permanently in spite of the conditions being changed to another type, were yet found to lose the acquired adaptations not suddenly but only in the course of three or more generations. A certain fern, *Adiantum*, is known to assume a very typical modification of form and structure, if grown on serpentine; now Sadebeck,[152] while cultivating this serpentine modification of *Adiantum* on ordinary ground, found that the first generation grown in the ordinary conditions loses only a little of its typical serpentine character, and that the next generation loses a little more, so that it is not before the fifth generation that all the characters of the serpentine modification have disappeared. There are a few more cases of a similar type relating to plants grown in the plains or on the mountains. There also it was found to take time, or rather to take the course of *several* generations, until what was required by the new conditions was reached. Of course these cases are very very few compared with those in which a *sudden* change of the adaptive character, corresponding to the actual conditions, sets in; but it is enough that they do exist.