248 Introduction to Botany. 



significance do you see in the different positions of the 

 flower in bud, after opening, and after pollination ? Sum 

 up those facts which relate to pollination. 



Asclepias cornuti (or other species). — Common Milkweed. 



Read the account of Asclepias cornuti on page 191. 

 What is the nature of the underground parts .'' Describe 

 the leaves and inflorescence. Break off a leaf or stem 

 and note the exudation of latex. Notice later how the 

 dried latex protects the wound. Examine the exterior of 

 a flower. Can the pistils be seen .? Find the entrance to 

 the stigmatic chamber (see Fig. 108). Slip the point of 

 a needle into a stigmatic chamber and pass it upward 

 and out at the top, so as to remove the corpusculum and 

 attached pollinia (see Fig. 113). Notice the slit-like 

 opening into the anther cavities through which the pollinia 

 are extracted. Draw the pollinia as seen under a lens. 

 Study cross sections of a flower at different heights, and 

 construct a diagram showing the main facts learned. In 

 cutting the cross sections pollinia will frequently be seen 

 lying in the stigmatic chambers where they have been 

 deposited by insects, and in the older flowers pollen tubes 

 may be seen penetrating the apex of a style. Study the 

 construction of the spur-like nectar receptacles growing 

 from the stamens. Observe the behavior of insects at 

 work on the flowers. Catch a bee with pollinia adhering 

 to it and study with a lens the way in which the pollinia are 

 made fast to the insect. . Point out the deviations from the 

 simpler types which the parts of this flower have undergone, 

 and show the purposes which these modifications serve. 



Taraxacum officinale. — Dandelion. 



Is this plant annual, biennial, or perennial.? What is the 

 nature of its underground parts? What descriptive terms 



