OUTLINE OF STRUCTURAL BOTANY 47 
miliar; investigation has changed the comparative rank of many 
Families so that the newer arrangement differs not only in the 
reversal of the sequences, but in a more or less general rearrange- 
ment. 
Again, the text-books universally known in this country during 
the last half century and more, those of Gray and Wood, like others 
less generally used, employed the term Order for the grouping 
next higher than that of the Genus. The term Family is now used 
where Gray and Wood and their contemporaries used the term 
Order and this latter term is employed for a group of Families. 
Thus we have, in the main, returned to the method of classifica- 
tion of Antoine Laurent de Jussieu which was published in 1789, 
but with modifications such as more recent investigations have 
suggested. 
The arrangement most generally accepted at present is that of 
Dr. Adolph Engler,t which system, with few modifications, has 
been followed in this work. 
The system is based upon the principle of development from the 
more simple to the more complex. Yet it is not always practicable 
to follow in a direct line such an evolutionary principle, since evolu- 
tion has progressed along different lines. Hence, one line is fol- 
lowed to its highest point of development. For example, along the 
line of monocotyledonous plants the Orchid Family represents the 
highest degree of development. It is more highly specialized than 
many plants of the Class of Dicotyledons, yet because, on the whole, 
this latter Class contains the most complex organizations, the 
whole of the Class takes rank above the whole of the Class of 
Monocotyledons, including the Orchids. 
This system of arrangement reveals the beauty of the principle 
of development in the Plant Kingdom and by the gradual modifi- 
cations which contribute to the characters of the successive Families 
the student is presented with a panorama of the history of the 
plant world which not only charms by the beauty of its symmetry, 
but enables him with much greater facility to comprehend and 
remember the relationship of the groups which he studies than was 
possible by the former system. 
SOME OF THE CHARACTERS OF PLANTS USED AS 
THE BASES OF CLASSIFICATION 
Evidently in order to form a practical system of classification of 
1Dr. Engler is Professor of Botany and Director of the Botanical Gardens and 
Museums of Berlin. 
