=849.= In some of the tropical orchids the pollinia are set free when the insect touches a certain part of the flower, and are thrown in such a way that the disk of the pollinium strikes the insect’s head and stands upright. By the time the insect reaches another flower the pollinium has bent downward sufficiently to strike against the stigma when the insect alights on the labellum. In the mountains of North Carolina I have seen a beautiful little orchid, in which, if one touches a certain part of the flower with a lead-pencil or other suitable object, the pollinium is set free suddenly, turns a complete somersault in the air, and lands with the disk sticking to the pencil. Many of the orchids grown in conservatories can be used to demonstrate some of these peculiar mechanisms. [Illustration: Fig. 464. Spray of leaves and flowers of cytisus.] [Illustration: Fig. 465. Flower of cytisus grown in conservatory. Same flower scattering pollen.] =860. Pollination of the canna.=—In the study of some of the marvellous adaptations of flowers for cross pollination one is led to inquire if, after all, plants are not intelligent beings, instead of mere automatons which respond to various sorts of stimuli. No plant has puzzled me so much in this respect as the canna, and any one will be well repaid for a study of recently opened flowers, even though it may be necessary to rise early in the morning to unravel the mystery, before bees or the wind have irritated the labellum. The canna flower is a bewildering maze of petals and petal-like members. The calyx is green, adherent to the ovary, and the limb divides into three, lanceolate lobes. The petals are obovate and spreading, while the stamens have all changed to petal-like members, called _staminodia_. Only one still shows its stamen origin, since the anther is seen at one side, while the filament is expanded laterally and upwards to form the _staminodium_. [Illustration: Fig. 466. Spartium, showing the dusting of the pollen through the opening keels on the under side of an insect. (From Kerner and Oliver.)] =861.= The ovary has three locules, and the three styles are usually united into a long, thin, strap-shaped style, as seen in the figure, though in some cases three, nearly distinct, filamentous styles are present. The end of this strap-shaped style has a peculiar curve on one side, the outline being sometimes like a long narrow letter S. It is on the end of this style, and along the crest of this curve, that the stigmatic surface lies, so that the pollen must be deposited on the stigmatic end or margin in order that fertilization may take place. [Illustration: Fig. 467. Cypripedium.]