THE FLOWER 91 



The spike has a very long axis, the flowers are sessile (i.e., 

 without pedicles) and usually crowded, as in the plantain, mul- 

 lein and wheat. 



The head has a very short axis, the flowers are sessile and 

 so crowded as to form a dense cluster, as in the case of the dande- 

 lion, sunflower, button bush and plane tree. 



The spadix is a very fleshy spike, such as is found in the 

 Indian turnip and calla. It is usually more or less enclosed by 

 an enlarged sheathing bract, or leaf-like structure known as the 

 spathe (Fig. 69). 



The catkin or ament, a scaly spike bearing either staminate 

 or pistillate flowers. They are usually pendent and are charac- 

 teristic of the willows, poplars, oaks and many other trees. The 

 staminate catkins are more common than the pistillate. 



The cyme is similar to the raceme except that the order of 

 blooming is the reverse. In most cases the lower peduncles are 

 longer than the upper, which brings all of the flowers on very 

 nearly the same level. In the scorpioid type the branches are 

 alternate, while in the Jielicoid type the branches arise from one 

 side and thus give rise to a curved flower axis. 



The types of flowers and inflorescence are illustrated in 

 Part III. They may be studied at this time or at such later 

 period in the course as may be most convenient. 



LABORATORY EXERCISES. 



Exercise 1. Use any complete flower in which all the parts are easily 

 recognized. Note the relation, size and shape of the sepals and petals, and 

 the arrangement of all the parts. 



Note the parts of the stamens and pistils. 



Examine the pollen under the microscope. 



Examine cross and longitudinal sections of the ovary. Determine the 

 number of carpels and union. How are the ovules attached? Estimate 

 the number of ovules. 



Exercise 2. Different types of flowers can be studied at such time as 

 may be most satisfactory. 



Exercise 3. Examine the pollen grains of several flowers, using the 

 compound microscope. 



