FLOWERS AND INSECTS 
129 
least two forms of flowers, which differ from one another 
in the relative lengths of their stamens and styles. In the 
accompanying illustrations of Houstonia (see Fig. 135) it 
is to be noticed that in one flower the stamens are short 
and included in the tube, and the style is long and pro- 
jecting, with the four stigmas exposed well above the 
tube. In the 
other flower the 
relative lengths 
are exactly re- 
versed, the 
style being 
short and in- 
cluded in the 
tube, and the 
stamens long 
and projecting. 
It appears that 
the pollen from 
the short sta- 
mens is most 
effective upon 
the stigmas of 
the short styles, 
and that the 
pollen from the 
long stamens is 
most effective 
upon the stig- 
mas of the long styles ; and as short stamens and long 
styles, or long stamens and short styles, are associated in 
the same flower, the pollen must be transferred to some 
other flower to find its appropriate stigma. This means 
that there is a difference between the pollen of the short 
stamens and that of the long ones. 
In some cases there are three forms of flowers, as in one 
FIG. 135. Flowers of Houstonia, showing two forms of 
flowers. In 1 there are short stamens and a long style ; 
in 2 long stamens and short style. An insect visiting 1 
will receive a band of pollen about the front part of its 
body ; upon visiting 2 this band will rub against the 
stigmas, and a fresh pollen band will be received upon 
the hinder part of the body, which, upon visiting another 
flower like No. 1, will brush against the stigmas. 
After GRAY. 
