366 BOTANY PART n 



orders. While some of the classes and orders thus constituted represent naturally 

 related groups, although by the method of their arrangement in the artificial 

 system they are isolated and widely removed from their proper position, they 

 include, for the most part, plants which phylogenetically are very far apart. 



LINNAEUS himself (1738) felt the necessity of establishing natural 

 families in which the plants should be arranged according to their 

 "relationships." So long, however, as the belief in the immutability 

 of species prevailed, the expressions relationship and family could 

 have no more than a hypothetical meaning, and merely indicated a 

 supposed agreement between plants having similar external forms. 

 A true basis for a natural system of classification of organisms was 

 first afforded by the theory of evolution. 



The system adopted as the basis of the following description and 

 systematic arrangement of plants is the natural system of ALEXANDER 

 BRAUN, as modified and further perfected by EICHLER, ENGLER, 

 WETTSTEIN, and others. 



The vegetable kingdom may be divided into the following four 

 main groups : 



1. Thallophyta. 



2. Bryophyta. 



3. Pteridophyta. 



4. Spermatophyta. 



DIVISION I 

 THALLOPHYTA. BRYOPHYTA. PTERIDOPHYTA 



Since the time of LINNAEUS the Thallophytes, Bryophytes, and 

 Pteridophytes have been termed collectively Cryptogams in contrast 

 to the Phanerogams or Spermatophyta. These two main divisions are, 

 however, of unequal systematic value, for the lower Phanerogams 

 approach the Pteridophyta, from which they have originated, more 

 closely than these most highly developed Cryptogams approach the 

 Bryophyta. The Bryophyta and the Thallophyta agree in being 

 composed of more or less uniform cells, and are contrasted as CELLULAR 

 PLANTS with the VASCULAR PLANTS comprising the Pteridophyta and 

 Spermatophyta. Since, however, the Bryophyta and Pteridophyta 

 agree in many respects, and appear to have diverged from a common 

 source, the distinction of cellular and vascular plants must not be too 

 strongly insisted upon. 



The Spermatophyta are distinguished by their distribution by 

 means of SEEDS from the Cryptogams, which form SPORES. Spores 



