394 VARIOUS PLANT GROUPS 



stantially that of Engler and Prantl whose great work on the 

 natural famiUes 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, thirtj'-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 ])rovided 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. 

 (Pteridophyfa). 



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 

 nuu'h 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 adoi)ted at the 

 present day. 



