LESSONS WITH PLANTS 341 



trees lean toward the lighter side. This is an effect of one- 

 sided illumination. 



Many plants assume definite attitudes during the night, 

 as if they went to sleep. Note the position of the leaves of a 

 young bean exposed to the light. Compare with another 

 kept in the dark for a number of hours. In the dark the 

 leaflets are more or less folded down and together and held 

 closer to the stem. The oxalis, sweet clover, and other 

 plants have similar habits. 



Many flowers open and shut under the influence of light 

 and darkness. We all know that the morning-glory opens 

 early in the morning. The dandelion " wakens with the 

 dawn." The four-o'clock remains shut until late in the af- 

 ternoon. 



The opening and closing of flowers may be partly due to 

 the Hght and darkness, but not entirely so. Some plants 

 seem to be regulated by the time of flight of the insects de- 

 pended upon for pollination. Some flowers that open only 

 at night are pollinated by moths and other nocturnal insects. 



Instead of closing at night, many flowers simply droop 

 or nod, and they do this also in the daytime to keep out the 

 rain. 



Some plants are excellent climbers. Some, like the peas, 

 hold themselves to their support by means of tendrils. 

 These are sensitive to the touch, and when they feel the 

 support as they wave around in the air in search for it, 

 will quickly curl around it. Other interesting tendrils are 

 those of the wild cucumber and of the Virginia creeper or 

 woodbine. One variety of the woodbine, the "self-clinging" 

 kind, has tendrils that, as soon as they touch the support, 

 spread out at the tip into little sucker disks that attach 



