Robertson — Flowers and Insects — Labiate. 127 
original type and readily to induce departures of a more seri- 
ous nature is an aggregation of the flowers in a more or less 
close cluster. In this case the lower lip loses its distinctive 
function both as a vexillary organ and as a landing-place. 
Both offices are immediately assumed by the inflorescence itself. 
As long as the flowers remain separate, they attract the insects 
which are pleased by the special floral form and are adapted 
to it. But when the flowers become clustered they attract 
less specialized insects to what appears an undifferentiated 
color mass. In a similar way, separated flowers are only 
readily visited by insects to which the lower lip forms a con- 
venient resting-place. But when the flowers form a compact 
inflorescence, a landing-place is formed by the flower-cluster. 
Even when the floral structure remains the same, I always 
expect to find less specialized insects on crowded flowers. 
As long as the cluster retains a spicate form, less specialized 
insects are not so well suited as when the inflorescence becomes 
flat-topped. In this case, these insects are afforded a con- 
venient landing-place, and insects which would never notice a 
separate flower of the same form will rest with ease upon the 
broad horizontal platform afforded by the aggregated flowers. 
But while the aggregation of the flowers is likely to induce 
the visits of less specialized insects, it makes easy other ad- 
vantageous modifications correlated with the relief of the 
lower lip from its normal function. It permits a reduction in 
the size of the flower, or a contraction of its parts, with the 
result that the nectar may be more deeply concealed and 
the place of pollen-contact may become limited to the upper 
part of the bee’s head or proboscis. 
This specialization, however, is conditioned upon the reten- 
tion by the galea of its normal function. For if the galea 
becomes reduced or reflexed in such a way as to expose the 
anthers and stigma, crowding results in changing the pollen- 
contact from the definite and precise noéotrive style to the 
indefinite style characteristic of the least specialized regu- 
lar flowers. If a Labiate flower typical in all other respects 
and separated from other flowers should come to have its 
anthers so exposed that insects could land upon them, it 
might be expected to change from nototribe to sternotribe, a 
