POLLINATION AND FERTILIZATION 145 
138. The periwinkle; a flower with concealed nectar. The 
common periwinkle,! a familiar old-fashioned flower, is an ex- 
cellent illustration of one way in which nectar is concealed 
and protected from undesirable insect visi- 
AWA tors. The tube of the corolla is moderately 
re \ ca long and is partly closed hy a sort of disk- 
car | shaped enlargement of the style (fig. 129). 
; Part of the under surface of the disk does 
Fre. 128. Flowerof the work of a stigma. 
potata, with widely The disk is surrounded by gummy mate- 
expanded corolla ‘ - 
rial and bears a crown of hairs at the top. 
The anthers open inward and so fill the crown of hairs with 
pollen. The long, slender tongue of an insect visitor (fig. 130), 
in being thrust through the fringing hairs and down the tube 
in search of nectar at its base, becomes covered with pollen. 
In this way some of it will be 
left on the stigma of the next 
periwinkle flower visited, which 
will secure cross-fertilization. 
Many other instances of con- 
cealment of the nectar supply 
can be discovered by the obsery- 
ing student. One of the most 
obvious is in such flowers as 
anapd ts gon end ee eae Fie. 129. Lengthwise section of 
in which the two-lipped corolla flower of periwinkle (Vinca minor), 
is rather firmly closed, so that the corolla with a closed throat and 
it can only be pried open by qa with the nectar not accessible to 
oan most small insects 
moderately strong insect. 
There is a lange clase of diskshere esenson a he cle 
flowers in which the nectar is tar glands at the base of the ovary 
not so much concealed as out 
of the reach of ordinary insects, since it is at the bottom of 
a long and narrow corolla tube or in a slender spur of the 
corolla. Excellent instances of this are found in the flowers 
1 Vinca minor. 
