56 



NORMAL AND EXPERIMENTAL POLLINATION. 



into the next flower, these usually come in contact with the stigmatic 

 surface, which acquires more and more pollen with each visit. The hawk- 

 moths continue to come for an hour or so after dark, and perhaps later if 

 nectar is still available. They are not frightened by lights being thrown 

 on them and in consequence their movements can be readily followed by 

 means of a flashlight. 



EXPERIMENTS. 

 ARTIFICIAL FLOWERS. 



Crepe-paper flowers. — Artificial flowers were made of crepe-paper 

 and provided with calyx-tubes of glass. Some of these were coated with 

 paraffin to stiffen them and others were shaped by stretching the paper. 

 The calyx-tube was filled with a sirup made of beet-sugar, and a drop of 

 nectar drawn from a flower placed at the top. The calyx-tubes of natural 

 flowers from which the nectar had been taken were then filled to the top 

 with sugar solution. In no case were the crepe-paper flowers visited or 

 even inspected, a fact difficult to explain, since the moths stopped to 

 inspect a white net and white pieces of paper lying near. The normal 

 flowers filled with sugar sirup were popular, and this was sipped as far down 

 as available. 



Petals obscured. — Flowers were covered with disks of green crepe-paper 

 with a hole cut at the center to allow the stamens and style to project and 

 also to permit access to the nectary. Thus, while the disk covered the white 

 petals, it did not confine the odor. No moths or other visitors stopped at 

 these flowers, although the calyx-tube in each case was well supplied with 

 nectar, while they came regularly to all the normal flowers among which 

 the experimental ones were located. They also stopped at the disks of white 

 paper that were grouped among the normal flowers. As the supply of flowers 

 became greatly reduced at the end of the season, frequent inspections were 

 made of the white-paper flowers. 



MENTZELIA MULTIFLORA. 

 NORMAL POLLINATION. 

 Habit and structure. — This species differs from most of the others 

 studied in that the flowers open at about 4 o'clock in the afternoon and 

 close about 8 at night. There is a distinct advantage in opening at this 

 time, since the nectar supply is running low in most of the flowers visited 

 during the day. About the time these flowers should open, several species 



Table 42. — Visitors and visits to normal flowers. 



