



INTRODUCTION. vii 



In addition to these main ranks, subordinate ones are sometimes employed, when further 

 division is desirable: thus a Class may be separated into Sulx-lasses, as the Claw Angio- 

 spermae into the Subclasses Monocotyledones and Dicotyledones; Families may be separated 

 into Tribes, as in the treatment of Gramineae in the following pages; Genera are often separ- 

 ated into Subgenera; and in the case of Species, where certain individuals are found to ex- 

 hibit features of structure or aspect differing more or less constantly from the majority of 

 the kind, these are set off as Varieties or Subspecies. Often the varieties or subspecies are 

 subsequently found to be distinct species. 



The variability of some species, caused by the operation of the forces collectively known 

 as the factors of organic evolution, is so great, and the variation Wing often toward a re- 

 lated species, that it is sometimes very difficult to determine whether certain individuals be- 

 long to one or to the other, or to a variety of one or the other. This leads to different opin- 

 ions. The actual fact, whether of the same species or not, may usually be ascertained by the 

 close examination of a large number of specimens, or by growing the formn in question ride 

 by side, when, if they are the same, their rapid approximation will be manifest; though if 

 their natural habitats are in different soils, this latter experiment may not be a satisfactory ttit. 



The grouping of Species into Genera, and of Genera into Families, though based upon 

 natural characters and relationships, is not governed by any definite rule that can be drawn 

 from nature for determining just what characters shall be sufficient to constitute a Onus or 

 a Family. These divisions are, therefore, necessarily more or less arbitrary and depend upon 

 the judgment of scientific experts, in which natural characters and affinities, as the most im- 

 portant and fundamental factors, do not necessarily exclude considerations of scientific con- 

 venience. The practice among the most approved authors has accordingly been various. 

 Some have made the number of genera and families as few as possible. This results in as- 

 sociating under one name species or genera that present marked differences among 

 themselves. The present tendency of expert opinion is to separate more freely 

 convenient natural groups, as genera and families, according to similarity of structure, 

 habit, form or appearance. While this somewhat increases the number of these division*, it 

 has the distinct advantage of decreasing the size of the groups, and thus materially facilitates 

 their study. This view has been taken in this work, following in most instances, but not in 

 all, the arrangement adopted by Engler and Prantl in their recent great work, " N 

 liche Planzenfamilien," * not yet quite completed, in which all known genera are describecl. 



Systematic Arrangement. 



The Nineteenth Century closes with the almost unanimous scientific judgment that the 

 order of nature is an order of evolution and development from the more simple to the more 

 complex. In no department of Natural Science is this progressive development more marked 

 or more demonstrable than in the vegetable life of the globe. Systematic Arrangement 

 should logically follow the natural order; and by this method al.so, as now Kent-rally recog- 

 nized, the best results of study and arrangement are obtained. The sequence of !'.: 

 adopted 50 or 75 years ago has become incongruous with our present knowledge; and i 

 for some time past been gradually superseded by truer scientific arrangements in the later 

 works of European authors, f 



The more simple forms are, in general, distinguished from the moi 



organs or parts; (2) by the less perfect adaptation of the organs to the purposes they sb 

 serve; (3) by the relative degree of development of the more important organ-. 

 lesser degree of differentiation of the plant-body or of its organ- 

 antiquity, as indicated by the geological record; (6) by a considc : 

 embryogeny. Thus, the Pteridophyta, which do not produce set 

 the earth in Silurian time, are simpler than the Spermatophyta; tin 

 the ovules are borne on the face of a scale, and which are known froi- 

 onward, are simpler than the Angiospermae, whose ovules are borne in a d 

 which are unknown before the Jurassic. 



In the Angiospermae the simpler types are those whose flora 



* Berlin, 15 volumes, 1890-1896. 



t Engler und Prantl, " Natiirliche Pflanzenfamilien; \Vaniiinu. 



, 



Vines, "Student's Handbook of Botany, 1895:" Richtcr. rUmt.i- 

 von Deutschland, OEsterreich und der Scluv,-. '"me. 



undMittel-Deutschland, 1887;" Schlechtendahl, Lanprethal und Sclu-r. 

 fifth edition by Hallier, 1880-1885. 



