Xll 
PREFACE. 
adheres to the albumen in which their embryo lies, and that circum- 
stance has given rise to the name SYNORHIZM. The veins of their 
leaves, when they have any veins, are either simple or forked, in 
whicli respect they approach Endogens on the one hand, and Aero- 
gens on the other. And finally, their vascular system is very imper- 
fect compared with that of other Exogens of an equal degree of de- 
velopement. 
The other group, called RHIZANTHS, is far less correctly known, 
but it seems to stand as it were between-Endogens and Acrogens of 
the lowest grade, agreeing with the latter in the absence, or very im- 
perfect state of the vascular system, in a general resemblance to Fungi, 
and in the apparent seeds being mere masses of sporules ; but appa- 
rently according with Endogens in the ternary number of their floral 
envelopes, and in the presence of fully developed sexes. 
Certainly there is no possibility of obtaining such important primary 
groups as these by any kind of artificial contrivance. 
With regard to the groups subordinate to these, their nature will be 
found sufficiently explained in the body of the work. I would only 
here observe, that as the number of their characters is necessarily 
smaller than what are available for the higher classes, the distinctions 
between them are consequently less strongly marked, and apparently 
of a more artificial nature. It has, however, been a great object with 
me to render the groups as perfect as possible, in order, firstly, to 
simplify the explanation of vegetable affinity ; and secondly, to offer 
what facilities the subject will allow of in analyzing the natural orders. It 
is here, indeed, that Botanists have most to do ; and it is most earnestly 
to be hoped that those whose leisure and knowledge will allow them to 
do, so, will occupy themselves in defining, or at least, in limiting with 
all practicable accuracy, those collections of orders which are subordi- 
nate to the primary classes. My reasons for rejecting those of the 
French school have been already briefly explained in the Nixus plan- 
tarum, and will be the subject of special discussion in another place, 
where I shall have an opportunity of going into the general question 
of the principles to be observed in Botanical Classifications further 
than would be possible on the present occasion. This, therefore, and 
all similar considerations I abandon for the present, confining myself 
now to a general explanation of the points to which this edition differs 
from the last, the bulk of which it very considerably exceeds. 
