14 INTRODUCTION. 



the great resemblance among them, the natural 

 affinity of the ancestral types being augmented by 

 characters produced by their being subjected to 

 the same surrounding medium. Even the other- 

 wise well defined- divisions of Monocotyledons, and 

 Dicotyledons, which both still exhibit fragmentary 

 proofs of their origin in the water, inosculate by 

 their aquatic members. Of the Gymnosperms, the 

 most ancient of Phanerogams, no aquatic forms 

 are known. They probably existed, but so long 

 ago as to have left no trace. 



Among the Monocotyledons, Lemna leads 

 through Pistia to the Aroidese and the Palms. Its 

 relative Naias connects through Alisma, with 

 Commelyna, and the Glumacese, as well as the Cor- 

 onarise; and by Stratiotes with the epigynous chain 

 of Mon jctyledons. Besides this the resemblance 

 of Alisma to the Kanuncnlaceous chain, with its 

 many aquatics, is more than a mere analogy, and 

 furnishes us with a link connecting the aquatic 

 Monocotyledons, and Dicotyledons. 



Podostemonere, Ceratophyllere, Callitrichace?e 

 are ancestral forms of Aphanocyclicse, and Tetra- 

 cyclicse. Hippuridse undeniable Perigynre, lead- 

 ing through Halorrhagide?e to Onagrarire, and 

 Myrtacere. So we find that the water has preserv- 

 ed a circle of ancestral forms from which have ra- 

 diated each of the great divisions of Angiosperms. 



2. An established numeric law indicates a 

 higher evolution than an indefinite number. For 

 instance, Pentandria and its multiples among Die- 



