164 Sprague . — On the He ter ant hits Section 
trees as are in flower, and only descend in numbers to the 
ground in open spaces. The reduction of the petals to two 
in certain species must be regarded as an adaptation to insect 
pollination rather than as a step towards total loss of petals, 
for it is significant that the two remaining petals are always 
the posterior ones, which are situated one on each side of the 
entrance to the nectariferous calyx spur ; the path to the 
honey is thus better marked after the loss of the four other 
petals. The same object is sometimes attained in the six- 
petalled species of Cuphea by having the two posterior petals 
much larger or differently coloured ; in C. rigidula they can 
be distinguished at once by the intense violet colouration 
of their claws. It is interesting to note that the reduction of 
petals does not always proceed regularly ; it might have been 
supposed a priori that the corresponding petals on each side 
of the flower would have disappeared simultaneously, but this 
is not the case, e. g. in C. tetrapetala , var. Cosangae , several 
of the flowers had three petals, the two dorsal and one 
lateral. It may be as well to state here that buds were 
examined in every case, to eliminate risk of error from the 
fugacious nature of the petals. 
The function of the disc needs investigation ; formerly it 
was thought to be the honey-producing part of the flower, 
and was called the gland, but Kerner (2) showed that this 
idea was erroneous and that the honey is really secreted by 
the base of the spur. The only explanation since given is 
that the disc helps to narrow the entrance to the spur, and 
thus aids in the exclusion of unbidden guests ; while this may 
be true in some instances, it hardly seems to hold good for all 
the species of Cuphea. 
The exclusion of small creeping insects is thoroughly 
effected in certain species of Cuphea , e. g. C. micrantha , which 
has the intersepaline teeth provided with glandular hairs. 
In the section Heteranthus no such efficient protection exists, 
but the axis of the raceme and the exterior of the calyx of 
all the species are more or less densely clothed with hairs, 
C. hispidijiora being especially well provided in this respect. 
