In the Angiosperms I have retained the sequence of orders in the Danish original, and have not rearranged them according to the systems more familiar to English students. In any rearrangement much of the significance of Dr. Warming’s valuable and original observations would have been lost, and also from a teacher’s point of view I have found this system of great value. Although at present it may not be completely satisfactory, yet as an attempt to explain the mutual relationships, development and retrogression of many of the orders, it may be considered to have a distinct advantage over the more artificial systems founded upon Jussieu’s Divisions of Polypetalæ, Gamopetalæ, and Apetalæ. With reference to the principles of the systematic arrangement adopted, I may here insert the following brief communication from the author (dated March, 1890), which he has requested me to quote from the preface of Dr. Knoblauch’s edition:--“Each form which, on comparative morphological considerations, is clearly less simple, or can be shown to have arisen by reduction or through abortion of another type having the same fundamental structure, or in which a further differentiation and division of labour is found, will be regarded as younger, and as far as possible, and so far as other considerations will admit, will be reviewed later than the ‘simpler,’ more complete, or richer forms. For instance, to serve as an illustration: EPIGYNY and PERIGYNY are less simple than HYPOGNY; the Epigynous _Sympetalæ_, _Choripetalæ_, _Monocotyledones_ are, therefore, treated last, the _Hydrocharitaceæ_ are considered last under the _Helobieæ_, etc. ZYGOMORPHY is younger than ACTINOMORPHY; the _Scitamineæ_ and _Gynandræ_ therefore follow after the _Liliifloræ_, the _Scrophulariaceæ_ after the _Solanaceæ_, _Linaria_ after _Verbascum_, etc. FORMS WITH UNITED LEAVES indicate younger types than those with free leaves; hence the _Sympetalæ_ come after the _Choripetalæ_, the _Sileneæ_ after the _Alsineæ_, the _Malcaceæ_ after the _Sterculiaceæ_ and _Tiliaceæ_, etc.