2 THE DEADNETTLE. [CHAP. 



What regulates the length of the tube ? What is 

 the use of this arch ? What lessons do these lobes 

 teach us ? What advantage is the honey to the 

 flower ? Of what use is the fringe of hairs ? Why 

 does the stigma project beyond the anthers ? and 

 why is the corolla white, while the rest of the plant 

 is green ? 



FIG. 2. Flower of Lainium alktm. FIG. 3. Section of ditto. 



Similar questions may of course be asked with 

 reference to other flowers. Let us now see whether 

 we can throw any light upon them. 



At the close of the last century, Conrad Sprengel 

 published a valuable book on flowers, in which he 

 pointed out that the forms and colours, the scent, 

 honey, and general structure of flowers, have reference 

 to the visits of insects, which are of importance in 

 transferring the pollen from the stamens to the pistil. 

 This admirable work, however, did not attract the 

 attention it deserved, and remained almost unknown 

 until Mr. Darwin devoted himself to the subject. Our 

 illustrious countryman was the first clearly to perceive 

 that the essential service which insects perform to 

 flowers consists not only in transferring the pollen 



