WATER-ABSORPTION AND TRANSPIRATION. 127 



QUESTIONS ON CHAPTER V. 



1. What chemical substance forms the great bulk of the weight 

 (a) of a living plant, (6) of a plant-body after it has been thoroughly 

 dried in an oven ? If the dried body is now carefully burned and the 

 ash collected, of what substances will it be found to consist, and what 

 has been lost in the process of burning ? 



2. How would you yourself determine the percentage of water and 

 the percentage of ash present in a plant? Name the elements most 

 generally present in a plant, and state how you would determine 

 which of these elements were absolutely necessary to the life of the 

 plant. 



3. How would you determine the best strength for a culture solution ? 

 How would you discover if the strength of the solution was altered by 

 the growth of the plant in it ? 



4. Explain how you would proceed to make a water culture. Indi- 

 cate the effect, on the plant, of the omission of salts containing calcium, 

 potassium, and nitrogen respectively. 



5. How are water-cultures carried on ? What are the commonest 

 causes of failure, and how may they be guarded against ? 



6. Pea seedlings with their roots in distilled water will sometimes 

 grow and produce leaves and flowers. Name the elements that the 

 plant must have obtained from some source or other, and explain how 

 the feeding of the plant in this case must have (a) agreed with, and 

 (6) differed from, that of a Pea seedling grown in earth. 



7. In what form is (a) hydrogen and (6) nitrogen absorbed by a 

 plant ? 



Explain as fully as possible the part played by each of these elements 

 in the economy of a green plant. 



8. Give results of actual experiments which show that seedlings of 

 common green plants are nourished (a) by air and sunlight, (b) by 

 substances taken up from the ground. 



9. What are the essential elements of an ordinary green plant's 

 food ? In what forms are these elements obtained ? 



10. What is meant by "water-culture"? Name the substances 

 which are used in making up a culture-solution for a green plant. 



11. Describe the method by which the importance of the various 

 mineral constituents of a plant's food has been most satisfactorily 

 ascertained. 



12. What materials compose the food of plants? Explain the dif< 

 ferences you have observed between the nutritive processes of a young 

 seedling and those of an adult plant. 



