ROBERTSON FLOWERS .t INSECTS — -UMBELLIFER^. 45 I 



is not a result of structural adaptation to them, but of the paucity of the 

 early fauna in lower hymenoptera. By referring to the table it will be 

 seen that only two other species show as many bees, viz., Zizia and Pas- 

 tinaca. In the first place, these are exposed to a more numerous bee-fauna. 

 But while Erigenia shows 27 bees in competition with i hymenopteron and 

 34 other species, Zizia shows 35 bees in competition with 32 hymenoptera 

 and 64 other species, and Pastinaca 30 bees against 97 hymenoptera and 

 148 other insects. In Erigenia bees are nearly 2< in Zizia nearly J, in 

 Pastinaca less than i of the number of visitors. 



Erigenia agrees with all of the earlier species, except those with con- 

 cealed nectar, in showing a preponderance of flies over hymenoptera, and 

 this is also a lesult of the absence of competition of the lower hymenop- 

 tera. The list of visitors is peculiarly rich in bees of the genus Andrena, 

 another result of early blooming. 



Chcerophyllum procumbens, Crantz. — The plant grows in rather thin 

 patches in dark woods. The umbels contain three or four small flowers, 

 which bloom in succession and are very inconspicuous. The flowers are 

 hermaphrodite, imperfectly proterandrous or homogamous, with short 

 stamens and styles. Sometimes I have found a dehiscent anther in con- 

 tact with the stigma, but even then most of the stigmatic surface remains 

 bare and ready to receive pollen from other flowers. However, all of the 

 flowers appear fruitful even in bad weather, so I think self-fertilization 

 always occurs in the absence of insects. 



The plant blooms next after Erigenia. The inconspicuousness of the 

 flowers is compensated for by a rich supply of nectar, so that I was ena- 

 bled to take 50 species of insects in three days. The nectar is more freely 

 exposed, and, as a consequence, we find fewer bees than in Erigenia and 

 an increased proportion of other insects. This is first to show Parasitica. 



Zizia aurea, Koch. — The plants grow in rather large patches, which 

 are made conspicuous by the yellow umbels. Five umbels of each order 

 produced an average of flowers and umbellets as follows : 



1st order — 294 male and 37 hermaphrodite flowers in 15 umbellets. 

 2d order — 170 •' " 178 '• " " iS " 



3d order — 89 " " loi " " " 14 '• 



The primary umbel commonly bears only male flowers : the proportion 

 of hermaphrodite flowers increases in umbels of 2d and 3d orders. The 

 fruitful umbellets have male flowers within, except a single central flower 

 which is hermaphrodite. The hermaphrodite flowers are proterogynous. 

 While the primary umbel is discharging pollen, the hermaphrodite flow- 

 ers of the secondary umbels protrude their receptive stigmas. Then they 

 and the male flowers discharge pollen to supply the first stage of flowers 

 of the umbels of the 3d order. 



The nectar is concealed by the inflected petals, and in the first stage 

 by the incurved stamens. This plant is |first to show Scoliidse, Pompi- 

 lidie, Crabronidse, and EumenidcE, which are now flying. The number 



