_Sempervivum tectorum_ and _S. montanum_, have long been noticed as being very prone to present this change. Mohl[346] remarks that, in the transformation of the stamens to the pistil in the common houseleek, the filament of the stamen generally preserves its form, the anthers alone undergoing change. At other times, however, the transformation takes place at the same time, both in the filament and in the anther. When the stamens are numerous some of them remain in their normal state, while others, and especially the inner ones, undergo a change. Sometimes all the stamens are changed simultaneously, while at other times some of these organs may be found in which the anther is partially filled with ovules, and partially with pollen. In the accompanying figures (fig. 165, _a-h_) a series of intermediate stages is shown between the ordinary stamen of _Sempervivum tectorum_ and the ordinary carpel, from which it will be seen that the filament is little, if at all, affected, and that in those cases where there is a combination of the attributes of the stamen and of the pistil in the same organ the pollen is formed in the upper or inner surface of the leaf-organ, while the ovules arise from the opposite surface from the free edge, (_b_, _c_, _d_, _e_, _f_, _g_). In a drawing made by the Rev. G. E. Smith of a malformed flower of _Primula acaulis_, and which the writer has had the opportunity of examining, the stamens are represented as detached from the corolla, and their anthers replaced by open carpels, with ovules arising, not only from their edges, but also from their surfaces, while the apex of the carpellary leaf was drawn out into a long style, terminated by a flattened spathulate stigma. _Delphinium elatum_ is one of the plants in which this change has been most frequently noticed.[347] [Illustration: Fig. 165.--_Sempervivum tecotorum._ _a._ Normal stamen. _h._ Normal carpel. _b_, _c_, _e_, _f_, _g_. Structure partly staminal, partly carpellary. _d._ Transverse section through _c_, showing pollen internally, ovules externally.] In willows the change of pistils into staminal organs has been frequently observed. In _Salix babylonica_ Prof. Schnizlein has described various transition stages between the carpels and the stamens, and in one instance, in addition to this change, a perfect cup-shaped perianth was present, as happens normally in _Populus_[348]. Mr. Lowe also records the conversion of stamens into ovaries in _Salix Andersoniana_, and this by every conceivable intermediate gradation.[349] The following list will serve to show what plants are most subject to this anomaly. It is difficult to draw any accurate inference from this enumeration, but attention may be called to the frequency of this occurrence in certain plants, such as the _Sempervivum_, the wallflower, the poppy, and the heath. Why these plants should specially be subject to these changes cannot be at present stated.