254 PLANT FAMILIES: DICOTYLEDONS. 



What is the homology of the cup ? i.e., to what part or series of members of 

 the plant does it belong ? Could the pistillate flower of the ancestors of the 

 oak have been in the form of aments, and if so could the cup of the acorn 

 represent the degraded and consolidated ament ? If so, what part of the 

 ament would now be represented in the cup ? (It has also been suggested 

 that the scales of the involucre which make up the cup are adventitious 

 growths accompanying the development of the fruit. ) 



(If the acorn has not been studied under the paragraph dealing with seeds 

 and fruits, and if there is time now, remove the wall of the acorn and deter- 

 mine the parts of the embryo. Are any parts of the embryo green while still 

 enclosed within the acorn ? 



Field observations on the oaks. — Compare the time of appearance of the 

 flowers and leaves of the oak. What about the abundance of the pollen ? 

 How are the oaks pollinated ? The ament-bearing plants are usually wind 

 pollinated, and for this reason there is an abundance of pollen, and always in 

 the form of dust. Is there an exception to this general rule ? How long 

 after the flowers are formed before the acorn is ripe ? 



If there is time during excursions note other ament-bearing plants. 



Material. — Mature leaves, leafy shoots, sprays of the flowers, both pistillate 

 and staminate ; fruit (the acorn in the cups). 



