INTRODUCTION 23 
(1) How does this flower prevent self-fertilization ? 
(2) How does this flower bring about cross-fertili- 
zation? 
(3) How does this flower prevent robbery of nectar 
or pollen by ants and other wingless insects? 
While the blossom of the Buttercup is very 
simple in structure, none of the floral elements 
being united to one another, the Evening Prim- 
rose may well serve to illustrate the structure of a 
flower in which the parts of the calyx seem to be 
grown together, although it is now thought that 
this tube represents not the united sepals but a 
band of leaf tissue. The long, light yellow blos- 
soms are borne on plants varying from one to 
three or four feet in height. The individual 
flower is frequently almost two inches long. 
The bud is protected by the greenish lobes of 
the calyx which separate and curl backward as 
the blossom opens: each lobe is nearly the shape 
of a long triangle; most of them fall off after the 
flower is fully open, in which case they are said 
to be caducous. There are generally four light 
yellow petals, delicate in texture, showing the 
slender veins and having the margin divided into 
shallow lobes. Within the petals are eight sta- 
mens with long filaments attached to the middle 
of the slender anthers. The pistil has a long and 
slender style on the end of which the stigma with 
its flattened lobes is borne; the latter is covered 
