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, Kolreuter 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 characteristics 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 define 

 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 

 FIG. 120. Flower of and 129) and is often stored at the base of 



p ?', v the corolla, sometimes in little pouches, as 



glands (n) at the base 



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 club-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. 



