EXERCISE 38 



Problem. Does light affect the direction of growth in a plant ? 



What to use. A geranium (or other potted plant) ; a sunny window. 



What to do. Notice position of flat surfaces of the leaves and upper tip of the plant in relation to 

 the window. Turn plant about 180 (halfway around). After twenty-four hours note carefully what 

 changes there are in the position of the leaves and of the tip. Repeat at intervals of one or two days, 

 until there is no doubt as to the relation between the light source and the growth of the plant. 



Record. Tell what happened and your conclusions. 





Questions. 1. Which parts of the plant seem to be most sensitive to light? 



2. Which side of the stem grew more rapidly, that in the light or that in the shade ? 



3. Try to tell how bending is brought about in the stem of the plant ? 



4. How are changes in position brought about in the leafstalk ? 



5. Do all plants behave the same way with relation to light? 



6. Of what use to the plant is the reaction of light? 



[43] 



