Robertson — Flowers and Insects — Labiate. 129 
inflorescences and deep tubes and ending with those having 
exposed stamens, flat-topped inflorescences and short tubes. It 
will be observed that as the most distinct Labiate characters are 
lost there is an increase in the proportion of lower hymenoptera 
and diptera visiting the flowers. As the tubes shorten and as 
the galea becomes less efficient as a protecting organ, there is 
an increase in the number of Andrenide@ which visit the flow- 
er for nectar and for pollen. As we descend the list in the 
table, bees remain the predominant visitors until we reach 
Monarda fistulosa which shows a preponderance of butterflies. 
After we pass Blephilia ciliata, bees cease to be the predomi- 
nant visitors, although the Pycnanthemums, except P. linifol- 
tum, show more bees than insects of other groups. Finally, 
the short tubed Mentha and Lycopus show lower hymenoptera 
in preponderance over bees, and flies more abundant than 
hymenoptera of any kind. 
In the case of the Umbelliferee, which have very uniform 
flowers, I have been able to show that the preponderance of 
bees, lower hymenoptera or diptera was determined mainly by 
the time of blooming, and the peculiarities in the lists of visi- 
tors were best shown by a table arranging the species in the 
order of blooming. A similar arrangement of the Labiatex 
does not give very important results, since the differences in the 
lists are mainly due to differences in structure, and the time 
of blooming has little influence. In the case of the Pyenan- 
themums, there seems to be a plain case of correlation between 
the form and arrangement of the flowers and the time of flight 
of the lower hymenoptera, which are very important visitors. 
If the flowers bloomed in April, the lower hymenoptera would 
be almost entirely wanting, and the list would consist mainly 
of bees and flies. 
Of the twenty-three species considered in the present paper, 
nine show long-tongued bees — Bombus, Synhalonia, Antho- 
phora and Melissodes — as their principal visitors and depend 
mainly upon them. Kight show special adaptation to bees 
in general or to shorter-tongued species. Early blooming 
species are visited by Bombus females, Anthophora, Synhai- 
onia, Osmia.and Alcidamea. Later blooming species are vis- 
