PREFACE. 
IX 
croscopical analyses, that some plants have spiral vessels, and others 
have none ; but it is not true, that in practice so minute and difficult an 
inquiry needs to be instituted, because it has also been ascertained that 
all plants that bear flowers have spiral vessels ; and that vegetables 
which have no flowers are usually destitute of spiral vessels, properly so 
called ; so that the inquiry of the student, instead of being directed 
in the first instance to an obscure but highly curious microscopical 
fact, is at once arrested by the two most obvious peculiarities of the 
vegetable kingdom. 
Among flowering plants two great divisions have been formed ; the 
names of which. Monocotyledons and Dicotyledons, are derived from 
the former having usually but one lobe to the seed, and the latter two, 
— a structure much more difficult to ascertain than the presence or ab- 
sence of spiral vessels, and more subject to exceptions. But no bota- 
nist would proceed to dissect the seeds of a plant for the purpose of 
detennining to which of these divisions it belonged, except in some 
special cases. We know that the minute organisation of the seed cor- 
responds with a peculiar structure of the stem, leaves, and flowers, the 
most highly developed, and most easily examined parts of vegetation ; a 
botanist, therefore, prefers to examine the stem, or the leaf of a plant, to 
see whether it is a Monocotyledon or a Dicotyledon, and does not find 
it necessary to anatomise the seed. 
The presence or absence of albumen, the structure of the embryo, 
the position of the seeds or ovules, the nature of the fruit, the modifica- 
tions of the flowers, are not to be brought forward as other difficult 
points peculiar to the study of the Natural System, because, whatever 
system is followed, the student must make himself acquainted with such 
facts, for the purpose of determining genera. The common Toad-flax 
cannot be discovered by its characters in any book of botany, without 
the greater part of this kind of inquiry being gone through. 
In the determination of genera, however, facility is entirely on the 
side of the Natural System. Jussieu has well remarked, that what- 
ever trouble is experienced in remembering, or applying the characters 
of natural orders, is more than compensated for by the facility of deter- 
mining'genera, the characters of which are simple in proportion as those 
of orders are complicated. The reverse takes place in arbitrary ar- 
rangements, where the distinctions of classes and sections are extremely 
simple and easy to remember, while those of genera are in proportion 
numerous and complicated.” 
