FOLIAGE LEAVES. 



401 



stem are turned so that they face the sun directly. In the morn 

 ing under the stimulus of the rising sun the rosette is formed 

 and faces the east. All through the day, if the sun continues to 

 shine, the leaves follow it, and at sundown the rosette faces 

 squarely the western horizon. For a week or more the young 

 sunflower head will also face the sun directly and follow it all 

 day as surely as the rosette of leaves. At length, a little while 

 before the flowers in the head blossom, the head ceases to turn, 



Fig. 440. 

 Same plant a little older when the head does not turn, but the stem and leaves do. 



but the rosette of leaves and the stem also, to some extent, con- 

 tinue to turn with the sun. When the leaves become mature 

 they also cease to turn. This is well shown in all three photo- 

 graphs (figs. 438-439). The lower leaves on the stem being 

 older have assumed the fixed horizontal position usually char- 

 acteristic of the plant with cylindrical habit. 



It is not true, as is commonly supposed, that the fully opened 

 sunflower head turns with the sun. But I have observed young 

 heads four or five inches in diameter rotate with the sun all day. 

 This is because the growing end of the stem as well as the young 

 head responds to the light stimulus. So there is some truth as 

 well as a great deal of fiction in the popular belief that the sun- 



