8 BOTANY AND PHARMACOGNOSY. 



THALLOPHYTES. 



The Thallophytes include the lowest orders of plants, 

 i.e., those simplest in form and structure. They are supposed also 

 to represent more or less primitive types. In these plants the 

 plant body does not show a differentiation into root, stem and 

 leaf, as in the higher plants, and is term.ed a thallus. The 

 thallus may branch in various ways, but the structure remains 

 more or less uniform throughout. It should be understood, how- 

 ever, that even in this group of plants certain cells or groups of 

 cells may become specialized, i.e., set apart for a particular func- 

 tion, as. for example, the reproductive cells. The Thallophytes 

 vary in size and general appearance from minute unicellular 

 organisms and those which are filamentous and delicately branched 

 to large leaf-like organisms many feet in length (Figs. 6, 9, 13). 



The Thallophytes are divided into the two groups of plants 

 known as (i) Algse and (2) Fungi. The Algae produce chloro- 

 plasts, and hence are capable of manufacturing food from the 

 inorganic substances air and water (see page 108), which fact 

 constitutes a fundamental difference betv/een them and the Fungi. 



ALG^. 



Algae are also characterized by their habit of living in water 

 or in moist places, and they are sometimes classified as " fresh 

 water algae " and " salt water algae " (Fig. 9). In the first group 

 are included the common pond-scums and certain forms living 

 on trees, moist rocks, fences and elsewhere, and in the second 

 group the sea-weeds. 



In addition to the chlorophyll (see page 159) of the chloro- 

 plasts other color substances are found in Algae, which mask the 

 green color to a considerable extent. On the basis of their color 

 Algae are subdivided into ( i ) Blue-green Algae or Cyanophyceae, 

 (2) Green Algae or Chlorophyceae, (3) Brown Algae or Phaeo- 

 phyceae, and (4) Red Algae or Rhodophyceae. While no attempt 

 will be made to consider these groups in detail, it should be 

 stated that they not only vary in color, but they also vary greatly 

 in structure and general appearance. A few type fomis will be 

 considered in order to illustrate their habits of life. 



