160 Introduction to Botany. 



and allow it to go to seed in this way. Tie a. bag over 

 another flower, while it is yet in bud, to keep foreign pollen 

 away, and when the flower has opened pollinate it with its 

 own pollen. Replace the bag and allow the flower to go 

 to seed. When the seeds in both experiments have formed, 

 compare the number and size of seeds produced by self 

 and cross fertilization. The larger the number of experi- 

 ments of this kind the more reliable are the results. 



129. Remove the petals from flowers which bees are 

 seen to visit frequently, and note whether the number of 

 the visits to the mutilated flowers is influenced by the 

 removal of the colored parts. 



130. Record the behavior of bees and butterflies in ob- 

 taining nectar or pollen from flowers, noting whether these 

 insects would be apt to be the cause of cross pollination. 



131. Make a record of some flowers which open only in 

 the nighttime. Do they become more fragrant at that 

 time ? Are they of light or dark hue ? What particular 

 sorts of insects visit them ? 



132. Make a record of some flowers which are open only 

 in the daytime. After closing at night do they open again ? 



133- Watch the behavior of the stigmas of . catalpa 

 flowers. At what stage in the development of the flowers 

 do the stigmas spread apart ? Do you find both open and 

 closed stigmas in the older flowers? Touch the open 

 stigmas with a brush or stick, and note their behavior. 

 Dust pollen on other open stigmas and note the result. 

 Do the stigmas behave alike in both cases ? The experi- 

 ment should be kept under observation for some time be- 

 fore the final record is made. 



134. Touch the bases of the filaments of barberry 

 flowers, and note the behavior of the stamens. Would 

 pollination be likely to occur without the aid of insects ? 



