138 INTRODUCTION TO BOTANY 
light, dust-like pollen, while others have pollen which coheres 
in sticky masses — and so on, with a multitude of other differ- 
ences. These singular facts were first explained in part by two 
eighteenth-century German botanists, Kélreuter and Sprengel, 
working independently of each other. Little was afterwards 
done to clear up the subject until Charles Darwin and a host 
of other investigators, beginning soon after the middle of the 
nineteenth century, worked out the details of the methods 
of pollination.1 
As a result of these studies it may be said that flowers owe 
most of their structural and other churucteristics to the fact that 
these things have enabled them to secure the needed pollination. 
130. Classification according to means of pollination. It is 
impossible in any brief way to give much of an account of the 
groups into which flowers are divided with reference to their 
means of securing pollination. Before out- 
lining these groups it is necessary to cefine 
the word nectar, This name is given to the 
sweet liquid found in many flowers — for 
example, columbine, honeysuckle, and red 
clover. The nectar is secreted by special 
organs known as nectar glands (figs. 120 
Fre. 120. Flowerof and 129) and is often stored at the base of 
Ente Bs erase the corolla, sometimes in little pouches, as 
of the ovary in the columbines and the honeysuckles. 
Some of the most important groups of 
flowers, classified according to their qualifications for securing 
pollination, are the following: 
1. Flowers mostly with inconspicuous perianth, and usually 
without nectar, destitute of odor, generally with moist or 
sticky pollen, with knob-like or elub-shaped stigmas. 
2. Flowers with inconspicuous perianth, destitute of odor, 
without nectar, with dust-like pollen, with feathery stigmas 
(fig. 121). 
1 See Knuth-Davis, Handbook of Flower Pollination, Vol. I. Clarendon 
Press, Oxford. 
