We pass insensibly from forms like these, to forms having bilateral symmetry strongly pronounced. Some such forms occur among flowers that grow at the ends of upright stems; as in _Pinguicula_, and in the Violet tribe. But this happens only where, in successive generations, the flower unfolds its parts sideways in constant relative positions. And in the immense majority of flowers having well-marked two-sided forms, the habitual exposure of the different parts to different sets of forces, is effectually secured by the mode of placing. As illustrations, I may name the genera--_Orchis_, _Utricularia_, _Salvia_, _Salix_, _Delphinium_, _Mentha_, _Teucrium_, _Ajuga_, _Ballota_, _Galeopsis_, _Lamium_, _Stachys_, _Nepeta_, _Marrubium_, _Calamintha_, _Melittis_, _Prunella_, _Scutellaria_, _Bartsia_, _Euphrasia_, _Rhinanthus_, _Melampyrum_, _Pedicularis_, _Linaria_, _Digitalis_, _Orobanche_, _Fumaria_, _&c._; to which may be added all the Grasses and all the _Papilionaceæ_. In most of these cases the flowers, being sessile on the sides of upright stems, are kept in quite fixed attitudes; and in the other cases the peduncles are very short, or else stiff enough to secure general uniformity in the positions. A few of the more marked types are shown in Figs. 234 to 241. [Illustration: Figs. 234–241.] [Illustration: Figs. 242–246.] [Illustration: Figs. 247, 248.] Very instructive evidences here meet us. Sometimes within the limits of one genus we find radial flowers, bilateral flowers, and flowers of intermediate characters. The genus