CHAPTEK XVI 



THALLOPHYTES: ALG^ 



152. General characters. — Thallophytes are the simplest of 

 plants, often so small as to escape general observation, but 

 sometimes with large bodies. They occur everywhere in 

 large numbers, and are of special interest as representing 

 the beginnings of the plant kingdom. In this group also 

 there are organized all of the principal activities of plants, 

 so that a study of Thallophytes furnishes a clew to the 

 structures and functions of the higher, more complex 

 groups. 



The word "thallus" refers to the nutritive body, or 

 vegetative body, as it is often called. This body does not 

 differentiate special nutritive organs, such as the leaves and 

 roots of higher plants, but all of its regions are alike. Its 

 natural position also is not erect, but prone. While most 

 Thallophytes have thallus bodies, in some of them, as in 

 certain marine forms, the nutritive body differentiates into 

 regions which resemble leaves, stems, and roots ; also cer- 

 tain Bryophytes have thallus bodies. The thallus body, 

 therefore, is not always a distinctive mark of Thallophytes, 

 but must be supplemented by other characters to determine 

 the group. 



153. Algae and Fungi. — It is convenient to separate Thallo- 

 phytes into two great divisions, known as Algm and Fungi. 

 It should be known that this is a very general division and 

 not a technical one, for there are groups of Thallophytes 

 which can not be regarded as strictly either Algae or Fungi, 

 but for the present these groups may be included. 

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