PLANTS MAKE FOOD 



89 



The experiment pictured shows this effect of light very plainly. 

 A hole was cut in one end of a cigar box and barriers were erected 

 in the interior of the box so that the seeds planted in the sawdust 

 received their light by an indirect course. The young seedling 

 in this case responded to the influence of the stimulus of light so 

 as to grow out finally through the hole in the box into the open 



Two stages in an experiment to show that green plants grow 



toward the light. 



air. This growth of the stem to the light is of very great impor- 

 tance to a growing plant, because, as we shall see later, food mak- 

 ing depends largely on the amount of sunlight the leaves receive. 

 Effect of Light on Leaf Arrangement. - - It is a matter of common 

 knowledge that green leaves turn toward the light. Place grow- 

 ing pea seedlings, oxalis, or any other plants of rapid growth near 

 a window which receives full sunlight. Within a short time the 

 leaves are found to be in positions to receive the most sunlight 

 possible. Careful observation of any plant growing outdoors 

 shows us that in almost every case the leaves are so disposed as 

 to get much sunlight. The ivy climbing up the wall, the morning- 

 glory, the dandelion, and the burdock all show different arrange- 

 ments of leaves, each presenting a large surface to the light. 

 Leaves are often definitely arranged, fitting in between one 



