REPRODUCTION AND DEVELOPMENT OF PLANTS 283 



FIG. 150. POTATO SPROUTS 

 GROWN IN A CELLAR 



This picture illustrates the 

 fact that a potato is an under- 

 ye" of the 

 bud which 



323. The Behavior of Flowers. Certain flowers, such as 

 the crocus and dandelion, open in the light and close in the 

 dark, whether it be at night or in cloudy weather. This 

 makes them ready to admit by day insect visitors, which 

 in their search for nectar receive pollen on their bodies to 

 be carried to other flowers. It also enables the flowers to 

 protect their pollen from dew by 



night or from possible rain on a 

 cloudy day. 



324. Motor Organs. The 

 old parts of some plants, being 

 too rigid to move easily, are 

 usually provided with special 

 structures to produce movement. 

 Examination of the base of the 

 leaf stalk of the bean, and also of 



the tiny stalks of the separate will develop into a branch bear- 

 leaflets, will show slight enlarge- ^ ^und. ^i. rromTh^ch^de 

 ments, which are called motor does the light come? How do 

 organs. These organs are com- 

 posed of cells containing much 

 water. Variations in the inten- 

 sity of light to which the bean 

 plant is exposed will cause rather prompt changes in the 

 amount of water in the cells of one part or another of the 

 motor organs. In the dark, the cells of the upper part of 

 the motor organs of the leaflets become full of water and so 

 the leaflets are made to droop. In the light, the reverse 

 conditions occur. 



325. Change of Response. The kind of response to 

 light stimulus may change at different stages of development 

 and growth. The flower stalks of a certain plant turn to- 

 ward the light when the buds first open and remain so until 

 after the pollination by insect visitors. Then, as they grow 

 longer, the stalks turn away from the light, and push their 



Men cut a potato into pieces be- 

 fore planting. Will every part of 

 a potato make a branch? Why? 



