86 PLANTS AND MAN 



Five phyla are often grouped together and known as the 

 thallus plants, or Thallophytes, since they are all characterized 

 by a relatively simple thallus body devoid of true roots, 

 stems or leaves; in no case do they produce flowers, fruits or 

 seeds. The phylum Schizophyta includes the simplest and 

 most primitive plants, such as the bacteria. The three phyla 

 Chlorophyta, Rhodophyta and Phaeophyta include those 

 species which form the bulk of the flora in both fresh and salt 

 water. The Mycophyta is made up of the chlorophyll-deficient 

 thallus plants commonly known as the fungi. 



The remaining three phyla are characterized by a more com- 

 plex vegetative and reproductive organization. These, in con- 

 trast with the preceding predominantly aquatic or microscopic 

 plants, are of larger size and comprise the major part of the land 

 vegetation. The phylum Bryophyta is made up of plants such as 

 the mosses, which have a rather imperfect vegetative body, as far 

 as adaptation to terrestrial life is concerned; while the phylum 

 Pteridophyta includes the ferns and their relatives, among 

 which the sporophyte body develops true roots, stems and leaves. 

 The most complex group of plant species constitutes the phylum 

 Spermatophyta, characterized by reproductive habits involving 

 flowers or cones, and seeds. 



The Thallus Spore Plants 



The thallus spore plants, or Thallophytes, include many 

 inconspicuous species rarely observed by the average person. A 

 great number are microscopiic, living their lives unseen in bodies 

 of water; others, though of larger size, exist beneath the surface 

 of the lakes and oceans. 



The simplest and yet the most iniquitous of all plants belong 

 to the phylum Schizophyta, characterized by a simple cell struc- 

 ture in which a true nucleus is lacking and limited to asexual 

 reproductive habits by fission. The 2500 known species are 

 grouped into two classes, in one of which chlorophyll is present, in 

 the other it is absent. The former comprises little-known slimy 

 water plants known as Blue-green Algae (fig. 56) while the latter 

 includes the Bacteria. 



