} 
PART III. | THE MECHANISMS OF FLOWERS. 257 
stalk of the ovary and fills the space between it and the sides of the 
tube. Insects are attracted from a distance by the crimson spikes 
of flowers, and are guided on their way to the honey by the dark 
red colour of the inner surface of the calyx and by the dark lines 
in the middle of each petal. These insects are caused to perform 
_ regular cross-fertilisation by the trimerphism of the flowers, which 
forms the most remarkable feature of the plant. 
In each flower the reproductive organs, which consist of one pistil 
and two whorls of stamens, of five or six each, are of three different 
i lengths ; the shortest are inclosed in the calyx-tube, the intermediate 
ones project 3 to 4 mm., and the longest 6 to 8 mm. beyond it, and 
either the style or one or other whorl of stamens may be the longest. 
_ All the flowers on any one plant are of the same kind, and the three 
forms are designated by Darwin, the Long-styled, Mid-styled, and 
ie Short-styled. Both pollen-grains and stigmatic papille differ 
according to the length of the organs which bear them. All the 
pollen-grains are elliptical when dry, and swell into a spherical form 
when moistened. The pollen-grains of the longest stamens are 
_ green, those from the middle-sized and shortest stamens are yellow. 
he pollen-grains vary in size also according to the length of the 
 stamen that they come from, and there is even a slight difference 
in size between pollen-grains from stamens of the same length but 
belonging to flowers of different kinds. The following table exhibits 
| these differences :— 
} | Size of dry pollen-grains | Diameter of 
ee el ee ee 
Length. Breadth. | in 335 mm. 
Long-styled . | Intermediate. | 74—84 4—4} 7—74 | Yellow. | 
| Long-styled . | Short . 1—74 34—4 6—64 | Yellow. 
| Mid-styled . | Long . 9—10 6—7 9—10 | Green. | 
_| Mid-styled . | Short . 6—7 34—4 6 Yellow. 
' | Short-styled . | Long . 10—11 6—8 94—104 | Green. 
| Short-styled . Intermediate. 7—8 4—5 7—74 | Yellow. 
So the longest stamens have the largést pollen-grains, and the 
hortest the smallest. 
: The pollen-grains of the long stamens differ more from those of 
e middle-sized and short stamens than these from each other. 
The stigmatic papille in the long-styled forms are considerably 
) longer and have their free ends farther apart than those in the 
| eo tyled and short-styled forms, which in this respect also do not 
S 
