THE LEAVES 57 



lord the sun is gone. If you cover the plant with a 

 box that admits no light, they will behave in the same 

 way. And now, watch a young sunflower that is 

 forming a flower-head. See how all the leaves near 

 the flower-head are drawn into a kind of rosette, and 

 how they all follow the sun round. Even the stem 

 that bears them moves round. Still later, when the 

 plant has many flowers, note how the flowers look to 

 the sun in the morning and see the last of him in the 

 evening, and how, after dark, the flowers droop and 

 look towards the earth. 



12. Most plants, when they have passed the growing 

 period, fix their leaves in the position where they are 

 likely to get most light. On cloudy days, a leaf with 

 its face turned full to the sky receives most light. 

 This will help you to understand the leaves of many 

 English trees. 



Questions and Exercises. — 



(1) Explain why you soon become stupid and sleepy in a room 

 which is not well-aired. 



(2) Why is air purer in a garden or wood than in a street. 



(3) Explain why a lamp goes out or burns badly if you fill up 

 the holes at the base of the lamp. 



(4) The leaves of the ordinary mallow weed are sensitive to the 

 light and follow the sun round. Put a stick into the ground in a 

 line with the midrib of one of the leaves on the morning of a sunny 

 day Place another stick in a line with the same midrib in the 

 evening. Note the angle that the leaf has passed through. 



Note. — The leaf must be one that swings clear of the ground 

 and of the other leaves. Leaves that are in the way can be 

 removed. 



(5) Compare the day-position and the night-position of the leaves 

 of the nasturtium and the lupine. 



(6) Some flowers shut early in the day, others later. Linnaeus, 

 a great botanist, tried to make a dial of flowers that would tell in 

 this way the time of day. Name some flowers that shut when 

 rain is threatening ; or in the evening. 



