2 1 2 EXPLAN A TOR Y INTR OD UCTION 
Abies, there is a list of names frequently met with in gardens, and 
opposite to each of these is given the name used in this work; thus 
Abies alba Michx. must be looked for under Picea, Abies Douglasii 
Lindl. under Tsuga, and so on. In the same way the genera are 
often much confused by synonymy. We have seen (Ch. II.) that it is 
very difficult to decide when the divergence of two forms is sufficient 
to entitle them to rank as genera, and this difficulty is the cause of 
much synonymy. A genus A is established by one author, and then it 
is discovered not to differ sufficiently from another genus B , established 
by the same or another author, to remain as an independent genus. 
A is therefore merged in B and becomes a synonym. The species of A 
retain as far as possible their old specific names when placed in B . 
When an entry such as “ Abelmoschus Medic. = Hibiscus Linn.” is 
found, it means that the genus Abelmoschus as established by Medicus 
is merged in Hibiscus of Linnaeus. In this case many of the species 
have entirely changed their names, e.g. A. venustus to H. spectabilis ; but 
some have retained their specific names, e.g. A. splendens has become 
H. splendens. This latter case is often indicated by putting the name 
of the old genus in brackets after that of the new, thus, H. (A.) splendens. 
In many cases the names of some of the genera thus merged in other genera 
are indicated thus: Apinm (Tourn.) Linn. (incl. Helosciaditwi Koch); 
no attempt however has been made to give all such cases or even a fraction 
of them, but only a few of the more important. In particular those have 
been given where the genus as here defined differs from the definition in 
Engler and Prantl’s Natiirliche PJlanzenfamilien by the inclusion or 
exclusion of other genera. [For further information as to nomenclature 
see Asa Gray’s Structural Botany , ch. x.] 
The name of the genus is followed by that of the natural order to 
which it belongs, and after this is often a number (in brackets) indi- 
cating the section of the order; thus Abelia belongs to Section ill of 
Caprifoliaceae, Acaena to Section III. 9 of Rosaceae. The general 
plan upon which the book has been constructed, and the necessity for 
condensation, render it essential, if the full advantage is to be derived 
from its use, that the student should refer to the natural order as well as 
the genus. There he will find the important general characters pos- 
sessed by the members of the order, and should examine the genus to 
see in what it agrees, and in what it disagrees, with these. A further 
reference to the classification given at the end of the article upon the 
order will point out the special characters to be looked for in the genus 
as a member of some particular sub-order or tribe. In this way a large 
amount of information about the particular plant in question may be 
obtained, and at the same time the student will get into the way of 
regarding plants not as so many independent and disconnected units, 
but as related members of one great whole. In this way too he 
will soon acquire an appreciation of the relative importance of the 
different characters in classification (see Ch. II) and will learn to 
