A YEAE IN SCIENCE 77 



or distilled water, in another. Evaporate the water in 

 each dish over the Bunsen flame. What is left in 

 each case ? How do you account for the difference ? 



B. In which kind of water do plants grow best? 



Fill one flask with well water and another with rain, 

 or distilled water. In each flask place "slips" of 

 Wandering Jew of about the same size. Change the 

 water in the flasks two or three times a week for 

 about a month. In which do the plants grow best? 

 What is the explanation? 



CHAPTER XIII 



PLANTS DEPENDENT UPON AIR AND MOISTURE 



Exercise 47. Gross Structure of Leaves. 

 Object: To study the parts of a leaf. 



Apparatus 



Lilac leaves Lily-of-the-valley leaves 



Directions : A. Parts. 



Carefully examine a lilac leaf. Make a drawing 

 of the leaf. Label the broad expanded portion, the 

 Made, and the stem by which it was attached, the 

 petiole. Compare the lengths of the petioles on a num- 

 ber of leaves on a lilac branch. From this observation 

 what is one of the functions of the petiole? The sur- 

 face of the leaf is provided with small openings or 

 pores, called stomates, through which the leaf respires. 



