PACHYLOPHUS CAESPITOSUS. 55 



o'clock in the evening just after opening, but before visitors were ob- 

 served. The absence of pollen on the stigmas furnished additional evidence 

 that they had not been visited. The nectar was blown out of the tube on 

 a glass slide and weighed immediately. 



Robertson (1892:272) has given a list of visitors to Oenothera biennis 

 and 0. fruticosa, and described the structure of the latter. The stigma 

 exceeds the anthers and is inclined to the lower side so that it strikes the 

 ventral surface of visiting bumble-bees. The tube measures 14 to 20 mm. 

 and can be drained only by the largest bees, though shorter-tongued ones 

 can reach a little of the nectar when the tube is fullest. Hitchcock (1893: 

 362) has observed that the stigma in Oenothera missouriensis may protrude 

 from the bud as early as 2 p. m., though the flower opens fully only during 

 the latter part of the afternoon. The narrow calyx-tube, about 11 cm. 

 long, is often half filled with nectar. With the exception of ants, the 

 only visitor was a sphinx-moth, Celerio lineata, which came in abundance 

 just before 8 p. m., but ceased its visits at dark. The insect pushed its 

 head into the throat as far as possible, but was able to reach only the upper 

 portion of the nectar, and was caught in the flower by its endeavor to secure 

 more. Merritt (1897:4) has noted that the flowers of 0. biennis open 

 about 6 p. m. and close about 9 a. m. While the stigmas are 2 to 6 mm. 

 beyond the anthers, a slight breeze is sufficient to bring them into contact. 

 By 7 h 30 m p. m. pollen was found on nearly all the stigmas, though no night 

 moths were seen. The odor is faint, but the large, pale flowers are con- 

 spicuous at night. In 0. californica the flowers at 6,000 feet are always 

 fully open by 5 p. m. and remain conspicuous and fragrant throughout 

 the night. Honey-bees collect pollen as soon as the flowers open and 

 usually strike the stigmas first, since the latter slightly exceed the anthers. 

 Nectar is not abundant at night, but by morning it is sometimes an inch 

 deep in the tube; the stigmas are visibly pollinated and the pollen is gone 

 from the anthers. Longyear (1909: 105) has described the opening of the 

 flower and its pollination in Oenothera pinnatifida. 



Behavior. — Three species of large hawk-moths come to the flowers 

 very soon after they open each night, namely, Protoparce quinquemaculata, 

 Hyloicus separatus, and Celerio lineata. The first two have a proboscis 

 9.5 to 10.5 cm. long, which enables them to reach to the bottom of the deepest 

 tube. It was found that each moth stays at a newly opened flower until 

 it obtains all the nectar that it can reach. Protoparce worked as long as 

 38 seconds at such flowers, but only 3 to 10 seconds at those that had been 

 previously visited. Celerio has a much shorter proboscis, about 4.5 cm. 

 long, and is limited to the nectar-supply in the upper half of the tube. 

 These moths fly swiftly through the air to a group of evening primroses, 

 when they stop over them, unroll the proboscis and hover in this position, 

 gradually descending until the tip of the ligule is above the opening to the 

 tube. After a few trials, the proboscis is gradually pushed down the tube 

 Until it reaches the nectar, after which it moves downward slowly as the 

 nectar is sipped up. When it has exhausted the nectar, the moth rises above 

 the flower and passes to the next. While poised in the air above the 

 flower after a visit, its proboscis is covered with large masses of pollen 

 and viscin threads at the point of contact with the anthers. When it dips 



