EXPLANATORY INTRODUCTION 
213 
recognise the approximate relationships of most plants after a brief 
inspection, or even at sight. 
The natural orders are those given by Engler in his Syllabus and in 
Die natiir lichen Pflanzen fa milieu (see Ch. II), but sufficient reference 
is made to Bentham and Hooker’s system of classification to enable 
any one who may prefer to use that system, or that of Eichler and 
Warming, to do so. 
The name of the natural order is followed by a statement of the 
number of species in the genus, and its geographical distribution. The 
number, unless very small, is always only an approximation; new 
research is always bringing new species to light, splitting up older 
ones, or combining two or more into one. This is all the information 
that is given about a very large number of the genera; only when 
a genus presents some character of interest which is not common to the 
order or group, is any particular mention made of it. The biological 
peculiarities of the most important genera are dealt with pretty fully, 
but much has been omitted. Thus in dealing with the pollination- 
methods of flowers a selection of important genera, illustrating the 
various methods, has been made for description in this part ; so too with 
epiphytes, xerophytes, the morphology of parts, and so on. General 
discussions of all these subjects will be found in Part I. and numerous 
examples are there quoted; these examples are mostly dealt with in 
full in this part. Innumerable cross-references to other articles and to 
Part I. are made, and should be looked up; those referring to Part II 
always quote the article and never the page, whilst those referring to 
Part I always quote the page, so that all references thus : p. 189, 
refer to Part I. 
While in the morphology &c. a selection has thus been made of 
genera for treatment, this is not the case with economic botany. This has 
been very fully treated, only a comparatively few genera being omitted. 
Space, however, has not permitted of a detailed description of economic 
products or the way in which they are obtained; for this reference 
must be made to other works (see Ch. IV). 
Turning now to the articles upon the natural orders, the same 
general principles apply to them. After the name of the order is given 
the cohort in Engler’s system to which it belongs. This should be 
looked up in Ch. II; this will show the orders which are most nearly 
related to the one under consideration, and the characters that dis- 
tinguish one from the other can be made out by comparison of their 
descriptions in Part II. The student should always endeavour to make 
out why a given order is classified in the position assigned to it. When 
the order as defined by Engler differs from that defined by Bentham 
and Hooker, as is so often the case, an attempt should be made to 
discover the reasons for the difference. 
After the position of the order in the system follows the number 
of its genera and species, the morphology and natural history of its 
