A SIMPLE FLOWER 83 



Self-Testing Exercise 



Protective coloring or resemblance is seen in the (1) 



(2) and (3). Protective mimicry is seen in the 



(4) and (5) butterflies. Insects are a (6) 



group. Many insects (7), and thus escape their enemies. 



The (8) stage is a help, because it provides a long quiescent 



(9) during which the insects are hidden from sight, Many 



insects are (10) colored. 



PROBLEM VH. OF WHAT USE ARE FLOWERS TO PLANTS? 



Laboratory Exercise. The structure of a simple flower. 



The floral envelope. Examine a simple flower, such as a lily. The 

 expanded portion of the flower stalk, which holds the parts of the 

 flower, is called the receptacle. The green leaflike parts covering the 

 unopened flower, when taken together, are called the calyx. Each of 

 these parts is a sepal. How many petals does your specimen have? 

 What use do they seem to have ? The more brightly colored structures 

 are the petals. How many do you find? When joined together, the 

 petals form a corolla. The corolla is of importance in making the flower 

 conspicuous. Of what value would this be? Frequently the petals or 

 corolla have bright marks or dots which lead down to the base of the 

 cup of the flower, where a sweet fluid called nectar is secreted by nectar 

 glands. It is principally this food substance, later made into honey 

 by bees, that makes flowers attractive to insects. 



The essential organs of the flower consist of the stamens and 

 pistil (or pistils), the latter being in the center of the flower. How 

 many stamens do you find in your specimen? Cut crosswise through 

 the swollen part of the pistil. How many divisions do you find? 

 Are the parts of the flower in multiples of each other? In a single 

 stamen the boxlike part at the end is the anther; the stalk which 

 holds the anther is called the filament. The anther is in reality a 

 hollow box which produces a large number of little grains called 

 pollen. Each pistil is composed of a rather stout base called the 

 ovary, which contains the ovule or future seeds, and a more or less 

 lengthened portion rising from the ovary called the style. The upper 

 end of the style is called the stigma. 



Practical Exercise 8. Draw a longitudinal section of the flower and label 

 all parts. Show the essential organs in color. 



Pollen. Pollen grains of various flowers, as seen under the micro- 

 scope, differ greatly in form and appearance. Some are relatively 

 large, some small, some rough, others smooth, some spherical, and 

 others angular. They all are alike, however, in having a thick wall, 

 with a thin membrane under it, the whole inclosing a mass of pro- 



