302 



THE CROSSING OF FLOWERS. 



up as the blossom fades, but the majority of Mezereon flowers stand out hori- 

 zontally from the branches, and in these it is hardly possible for the adhesive 

 pollen to reach the stigmas unaided, although the anthers and stigma are not 

 more than 2 mm. apart. Mezereon flowers are visited so industriously by bees, 

 however, that most of the stigmas are pollinated by strange pollen, and thus 

 manifold crossings are obtained. In the majority of Orchids, too, the pollen is 

 only brought from its hiding-place by insects which hardly ever deposit it on the 

 adjacent stigma, but as a rule transfer it to the stigma of another flower. 



Heterostyled plants present a peculiar condition. Many Gentianaceae (e.g. Meny- 

 anthes trifoliata, Gentiana Rhcetica and Germanica), the various species of Bastard 

 Toadflax (Thesium), numerous Primulaceae (e.g. Androsace, Aretia, Gregoria, Hot- 



Fig. 288. Heterostyled flowers. 



i Plant of Primula minima with a long-styled flower. 2 Plant of the same species with a short-styled flower. * Short-styled 

 flower of Pulmonaria qffleinalis. * Long-styled flower of Pulmonaria ojicinalis. Short-styled flower of JEschscholtzia 

 Californica. 6 Long-styled flower of the same plant. All nat. size. 



tonia, Primula, see figs. 288 l and 288 2 ) as well as many Boraginaceae (e.g. Myosotis, 

 Mertensia, Pulmonaria; see figs. 288 3 and 288 4 ) and members of other groups, 

 bear flowers with relatively short styles on one plant, the anthers being above the 

 stigma, while, on another plant of the same species, the flowers have all relatively 

 long styles, and the anthers are inserted below the stigma. At the opening of the 

 flowers the stigmas cannot receive pollen unaided either from the anthers above or 

 from those below them. But an insect, which, by inserting its proboscis into a 

 short-styled flower, has brushed against the anthers at the mouth of the corolla- 

 tube, and thus loaded itself with pollen, will deposit this exactly on the stigma of a 

 long-styled flower, should it enter one, since the stigma is just at the same level in 

 the second flower as the circle of anthers in the first-visited, short-styled form. In 

 the same way it is hardly necessary to say that the pollen, which has adhered to 

 the proboscis of a honey-sucking insect half-way up the corolla-tube of a long- 

 styled flower, will be deposited on the stigma which reaches the same level in a 



