viii INTRODUCTION. 
structure of the branch or stem from which the flower has been metamorphosed, that is to 
say, in which the parts of the flower (modified leaves) are more nearly separate or distinct 
from each other, the leaves of any stem or branch being normally separated, while those are 
the most complex whose floral parts are most united. These principles are applied to the 
arrangement of the Subclasses Monocotyledones and Dicotyledones independently, the 
Monocotyledones being the simpler, as shown by the less degree of differentiation of their 
tissues, though their floral structure is not so very different nor their antiquity much greater, 
so far as present information goes. For these reasons it is considered that Typhaceae, Spar- 
ganiaceae and Naiadaceae are the simplest of the Monocotyledones, and Orchidaceae the most 
complex; Saururaceae the simplest family of Dicotyledones, and Compositae the most complex. 
Inasmuch as evolution has not always been progressive, but some groups, on the contrary, 
have clearly been developed by degradation from more highly organized ones, and other 
groups have been produced by divergence along more than one line from the parent stock, 
no linear consecutive sequence can, at all points, truly represent the actual lines of descent. 
The sequence of families adopted by Engler and Prantl, in ‘‘ Natiirliche Pfhlanzenfam- 
ilien ’ above referred to, has been closely followed in this book, in the belief that their sys- 
tem is the most complete and philosophical yet presented. The sequence of genera adopted 
by them has for the most part also been accepted, though this sequence within the family 
does not attempt to indicate greater or less complexity of organization. 
It was originally intended to present a conspectus of the orders and families included in 
this work in the Introduction, as is indicated upon page 62 of this volume. But as the printing 
proceeded it was deemed better to place this at the end of the third volume. 
Nomenclature. 
The names of genera and species used in this work are in accordance with the Code of 
Nomenclature devised by the Paris Botanical Congress in 1867, as modified by the rules 
adopted by the Botanical Club of the American Association for the Advancement of Science 
at the meetings held at Rochester, New York, in August, 1892, and at Madison, Wisconsin, 
in August, 1893. These names were mostly elaborated in the ‘‘ List of Pteridophyta and 
Spermatophyta growing without Cultivation in Northeastern North America,’’ prepared by 
the Committee of that association and published in 1894 as the fifth volume of Memoirs of 
the Torrey Botanical Club. The synonyms given under each species in this work include 
the recent current names, and thus avoid any difficulty in identification. 
The necessity for these rules of nomenclature arose from the great confusion that has ex- 
isted through the many different botanical names for the same species or genera. Some 
species have had from ro to 20 different names, and, worse still, different plants have often 
had the same name. For about 200,000 known species of plants there are not fewer than 
700,000 recorded names. Such a chaotic condition of nomenclature is not only extremely 
unscientific, burdensome and confusing in itself, but the difficulty and uncertainty of identi- 
fication which it causes in the comparative study of plants must make it, so long as it con- 
tinues, a serious and constant obstruction in the path of botanical inquiry. 
The need of reform, and of finding some simple and fixed system of stable nomenclature, 
has long been recognized. This was clearly stated in 1813 by A. P. De Candolle in his Théorie 
Elémentaire de la Botanique (pp. 228-250), where he declares priority to be the fundamental 
law of nomenclature. Most systematists have acknowledged the validity of this rule. Dr. 
Asa Gray, in his Structural Botany, says (p. 348): ‘‘For each plant or group there can be 
only one valid name, and that always the most ancient, if it is tenable; consequently no new 
name should be given to an old plant or group, except for necessity.”’ 
This principle was applied to Zodlogy in the ‘‘ Stricklandian Code,’’ adopted in 1842 as 
Rules of the British Association, and revised in 1860 and 1865 by a committee embracing 
the most eminent English authorities, such as Darwin, Henslow, Wallace, Clayton, Balfour, 
Huxley, Bentham and Hooker. In American Zodlogy the same difficulties were met and 
satisfactorily overcome by a rigid system of rules analogous to those here followed and now 
generally accepted by zoGlogists and palaeontologists. 
At an International Botanical Congress held at Paris in 1867, in which unfortunately the 
English botanists did not participate, A. DeCandolle presented a system of rules which, with 
modifications, were adopted, and, as above stated, are the foundation of the present rules of 
the botanists of the American Association. ‘These rules were in part adopted also by the In- 
ternational Botanical Congress held at Genoa in 1892, and by the Austro-German botanists at 
