368 BOTANY: PRINCIPLES AND PROBLEMS 



806. What advantages have the angiosperms over the gymnosperms 

 which should have made them so much more successful? 



807. Give an example of a crop plant which is an annual herb; one 

 which is a biennial herb; one which is a perennial herb; one which is a 

 shrub; one which is a tree. 



808. Which of these five plant types is of most importance in agricul- 

 ture? Why? 



809. There is a larger proportion of herbaceous species in the flora of 

 a temperate region than in the flora of a tropical one. Explain. 



810. Angiosperms, and especially herbaceous angiosperms, have 

 apparently evolved much faster and given rise to many more species 

 than either pteridophytes or gymnosperms in a similar length of time. 

 Why? 



811. What evidence can you suggest for the conclusion that the 

 dicotyledons are more ancient than the monocotyledons? 



812. We believe that families in which the flowers are irregular are 

 usually more recent in evolutionary origin than those where the flowers 

 are regular. Why? 



813. We believe that a flower with a large and indefinite number of 

 floral parts, all free from one another, is more ancient in type than one 

 in which the number of parts is smaller and more constant and where 

 they are more or less united with one another. Why? 



814. In what respect may stamens and carpels be called "sexual 

 organs" and in what respect is it incorrect to call them such? 



815. What conclusion can you draw as to the relative osmotic concen- 

 tration of the cell sap in the pollen grains and in the cells of the stigma? 



816. Why do we regard the composite and the orchid families as 

 marking the highest points in the evolution of the plant kingdom? 



REFERENCE PROBLEMS 



138. What familj' is most important as a producer of food plants and what 

 are some of the notable crop plants included in it? Name a few other 

 families which have many important economic plants. 



139. Seed plants are sometimes known as the Siphonogamia. Whj' is this 

 name appropriate for them? 



140. The terms Cryptogams and Phanerogams are sometimes used to 

 designate two groups into which the plant kingdom may be divided, the 



