NATURAL SYSTEMS OF CLASSIFICATION. 416 
to be carried out varies according to the particular views of 
botanists as to the relative value of the characters furnished by 
the different organs of plants ; but it must be evident to those 
who desire to arrange plants according to their natural aftini- 
ties, that those systems of classification will be the most natural 
in which the organs of the highest value, and those least liable 
to change, are especially relied on in the determination of the 
affinities of plants. 
Taking these principles as our guide, we should regard the 
organs of reproduction as of the highest importance, and we find 
accordingly that while some plants have flowers with evident 
sexes, others have no flowers, and their sexual organs are more 
or less concealed ; hence the former are called Phanerogamous 
or Phzenogamous, and the latter Cryptogamous. The former 
are also reproduced by true seeds containing an embryo, whilst 
the latter are reproduced by spores in which we have no such 
structure as an embryo; hence these characters are of the first 
importance. 
Next in importance comes the presence or absence of an 
ovary, as such a difference is accompanied by essential structural 
and functional peculiarities, and we have thus the two great 
divisions of Angiospermous and Gymnospermous plants. 
Next in value is the structure of the embryo itself, as it con- 
tains within itself in a rudimentary condition all the essential 
organs of a plant. Hence as the embryo varies in the number 
of its cotyledons, cotyledonous plants are further divided into 
two classes—those possessing one cotyledon being called Mono- 
cotyledonous, and those with two, Dicotyledonous. 
Next in importance is the presence or absence of a stem, 
giving the names of Cormophytes and Thallophytes ; whilst in 
those with stems the internal structure and development pre- 
sents us with well-marked and important characters. 
The characters founded upon the position and relation of 
the stamens and carpels to each other, as also to the floral en- 
velopes ; as well as the presence or absence of one or both of 
the floral envelopes, and the union or otherwise of their con- 
stituent parts, although not of the highest importance, are of 
much value in the subordinate divisions. 
The leaf also is of some importance as regards its venation : 
thus, in Cormophytes the leaves or fronds have commonly a 
forked venation ; those of Monocotyledonous plants are parallel- 
veined ; while those of Dicotyledonous plants are net-veined or 
reticulated. Again, stemless plants have no true leaves, but 
produce a flattened cellular expansion or thallus, which has no 
true veins. 
Such are the general principles which should be attended to 
by those who arrange plants according to their natural affinities ;, 
but it must be borne in mind, that even in the best devised 
natural systems there must be (at least at present) much that is 
