102 THE COLOURS OF FLOWERS. 



Submerged or floating plants especially tend as a rule 

 to become green-flowered, and to grow very degraded 

 in structure. As instances, we may take Myrio- 

 phyllum, Ceratophyllum, Elodea, Lemna, Callitriche, 

 Potamogeton, Ruppia, and Hippuris. In most of 

 these groups the proofs of great degeneration are 

 too obvious to need insisting upon. 



There remain doubtful, then, among green Dico- 

 tyledons, only the highly anemophilous families, like 

 the nettles (Urticacece) , and the catkin-bearing trees 

 (Amentiferce]. The former have a well-developed 

 calyx, at least to the male flowers ; and it is difficult 

 to see how any one who compares them with Scleran- 

 thus or Mercurialis, known descendants of petaliferous 

 forms, can doubt that they too are degenerate types. 

 Indeed, the mere fact that the stamens are opposite to 

 the lobes of the calyx (Fig. 36), instead of alternate 

 with them, in itself shows that a petal-whorl has been 

 suppressed ; as is likewise the case in the goose-foots 

 and many other doubtful instances. Moreover, the 

 nettles are closely allied to the elms ( Ulmacetz), which 

 are obviously degenerate, and have acquired a coloured 

 perianth, side by side with their resumption of the 

 entomophilous habit. 



As to the Amentiferce, Cupuliferce, and other catkin- 

 bearers, at first sight we might suppose them to be 

 primitive green anemophilous orders. But on closer 

 consideration, we may see grounds for believing that 

 they are really degenerate descendants of entomo- 

 philous plants. In the alder (Alnus) the male catkins 

 consist of clustered flowers, three together under a 

 bract, each containing a four-tobed perianth, with four 

 stamens within (Fig. 37). These little florets exactly 



