394 VARIOUS PLANT GROUPS 
stantially that of Engler and Prantl whose great work on the 
natural families of plants is now most generally followed, at 
least, with regard to phenogams. In this classification there 
are recognized among seed-plants about fifty orders and two 
hundred and eighty families. 
The eighteen orders, thirty-two families, and about a hundred 
genera of seed-plants included in this chapter are represented by 
formulas on pages 404-427 in order that the student may readily 
compare the more important structural characters of one group 
with those of another, and so gain a better grasp of the abstract 
ideas underlying a natural classification. Taken in connection with 
the accounts of the various groups given in the sections referred to 
by number before each formula, and with reference to the figures 
indicated in each section, the formulas will afford a most profitable 
means of reviewing the many details already studied, and will re- 
veal some of their wider relations. 
162. The vegetable kingdom (Vegetabilia) which includes 
all plants is regarded most conveniently as consisting of 
four main divisions assumed to be equal in rank.} 
The highest division, that of seedworts or spermatophytes, 
includes most of the forms we have been studying. These 
agree not only in producing seeds but also in having true 
roots, stems, and mostly green leaves, all traversed by more 
or less woody strands, known as fibrovascular bundles, which 
form a framework or skeleton, and conduct nutrient juices - 
to every part. 
True roots, stems, and green leaves, all provided with 
fibrovascular bundles, occur also in such plants as the male- 
fern (Aspidium, page 179) and the club-moss (Lycopodium, 
page 174); but these plants propagate by spores developed 
in minute spore-cases, and never produce seeds. Plants thus 
characterized form the pteridophyte or fernwort division. 
(Pteridophyta). 
Next to these come such plants as peat moss (Sphagnum, 
page 242) which propagate by spores similar to those of fern- 
worts but contained in more or less urn-like cases commonly 
much larger than fernwort spore-cases, and usually borne on 
1 This view differs somewhat from that of Engler and Prantl, but 
best suits our purpose as being the one most widely adopted at the 
present day. 
