112 PROF. BOWER : 
for long after the publication of the ‘Origin of Species, the Natural 
Classification of Plants was still concerned rather with the distal twigs 
than with the main branches of the Evolutionary Tree. Even now, the 
question whether there was really a single trunk is unsettled, not only 
for the Vegetable Kingdom at large, but also for its chief Divisions. Such 
questions as the genetic relations of the Bryophytes and Pteridophytes : or 
of the Gymnosperms and Angiosperms: of the inter-relations of Mosses 
and Liverworts, or of the several phyla of Pteridophytes, are still matters 
of speculation rather than of demonstration. Nevertheless, the assembly of 
the members of each into genera, and groups of genera, is already well 
advanced. The sequence of steps is naturally backwards from species and 
genera to groups of genera, and orders: and thence to groups of orders. 
But the argument proceeds from the distal to the proximal with ever 
increasing uncertainty. Natural History is in fact like any other history— 
a cult which is liable to lose its precision as it extends backwards into the 
mists of the past. 
In 1909 the sixth edition of Engler's ‘Syllabus of the Families of 
Plants’ was published. It contains on its opening pages a statement of 
the “Principles of Systematic Arrangement." This, though not by any 
means exhaustive, may yet be taken as an Index of the point of view 
entertained exactly fifty years after the appearance of the ‘Origin of 
Species.’ It is true that it relates almost entirely to Flowering Plants, 
as is natural since Professor Engler has been chiefly engaged upon them. 
Using freely the observational results acquired by such predecessors as 
Braun, Eichler, Bentham, and Hooker, he has proposed extensive re- 
arrangements of the Families of Flowering Plants, in accordance with 
the phyletie views set forth in his Introduction to the Syllabus. Apart 
from those statements which have their special reference to Flowering 
Plants, he enunciates among his Principles some which are of general 
application. For instance, the facts of Ontogeny are held to be of the 
first importance, as reflecting the probable course of Descent. But it is 
pointed out that the facts of progress of individual organs from a phyletically 
early state to the advanced are not usually available. It is recognized that 
a character of value for comparison in one circle of affinity may be valueless 
in another. On the other hand, those characters which remain constant in a 
phylum are of special value in its comparative treatment. Insistently the 
question will arise whether parts relatively simple in character are actually 
primitive, or the result of reduction. The value of anatomical data is freely 
acknowledged ; but those characters which are not in direct relation to 
external conditions are to be estimated more highly than those referable 
to adaptation. Combinations of progression in characters independent of 
one another are recognized as specially important. Finally, the facts 
