INTRODUCTION 23 



(i) 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 wdiich 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 



