270 THE GEOLOGICAL HISTORY OF PLANTS. 



"But when we have reached the branch representing 

 the generic form we have made but little progress in the 

 phylogenesis of Salix. With Populus this genus forms 

 a small order, Salicineae. The two genera are closely 

 allied, yet separated by well-marked characters ; it is 

 not, however, difficult to conceive of both having sprung 

 from a generalised form. But there is no record of such 

 a form. The two genera appear together among the 

 earliest known dicotyledons, the willows being repre- 

 sented by six and the poplars by nine species. The or- 

 dinal form, if it ever existed, must necessarily be much 

 older than the period of the Upper Cretaceous rocks, 

 that is, than the period to which the earliest known 

 dicotyledons belong. 



"The Salicineae are related to five other natural 

 orders, in all of which the apetalous flowers are arranged 

 in catkins. These different though allied orders must 

 be led up by small modifications to a generalised amen- 

 tiferous type, and thereafter the various groups of apetal- 

 ous plants by innumerable eliminations of differentiating 

 characters until the primitive form of the apetalous plant 

 is reached. Beyond this the uncurbed imagination will 

 have more active work in bridging over the gap between 

 Angiosperms and Gymnosperms, in finding the interme- 

 diate forms that led up to the vascular cryptogams, and 

 on through the cellular plants to the primordial germ. 

 Every step in this phylogenetic tree must be imagined. 

 The earliest dicotyledon takes us not a step farther back 

 in the phylogenetic history of Salix than that supplied 

 by existing vegetation. All beyond the testimony of our 

 living willows is pure imagination, unsupported by a 

 single fact. So that here, also, the evidence is against 

 evolution, and there is none in favour of it." 



It is easy to see that similar difficulties beset every 

 attempt to trace the development of plants on the prin- 

 ciple of slow and gradual evolution, and we are driven 



