EXERCISES 311 



Seed plants produce true seeds, and, in trees and shrubs, produce 

 woody stems. 



Classes of seed plants are gymnosperms and angiosperms. 



Composite flowers are the highest form of plant organization. 



Economic plants are of great importance for man, in that they give 

 him food, clothing, shelter, and tools. 



Plants are distributed in great zones, corresponding to the zones of 

 temperature. 



331. Exercises. 



1. What precautions are necessary, in the canning of fruit, to keep 

 it from spoiling? Why? Why are meat, milk, compressed yeast, etc., 

 kept in cold refrigerators? 



2. How do preservatives, like formaldehyde, borax, etc., prevent 

 the decay of food? If digestion is a series of fermentations (cf. 368), 

 will a food containing preservatives be easily digested? 



3. Why do not fungi produce chlorophyll? When a potato sprouts 

 in a dark cellar, why are its leaves and leaf stalks white? How is 

 celery bleached? 



4. Is it a good plan to put away fresh, warm bread in a covered 

 box? W T hy? 



5. Do you think it possible that some of our wild grasses might be 

 cultivated so as to become useful grains? How could this be done? 

 What fruits have been developed by the cultivation of inferior or wild 

 varieties? 



6. Many plants in the tropics have thick-walled leaves with tips 

 in the form of gutters. To what two sets of conditions have they 

 adapted themselves? 



7. Why is it necessary for the leaves of evergreens growing in cold 

 climates to be thick and needle-shaped rather than thin and spreading? 



8. What are some commercial uses of moss? 



9. How does the cultivated rose differ from the wild rose? Ask a 

 gardener whether the cultivated rose can be reproduced from seeds. 



