DEVELOPMENT OF PLANTS 



149 



marine life. The Diatoms are unicellular plants and exhibit 

 a great variety of forms as circular, elliptical, rod or wedge- 



FIG. 94. Common forms of diatoms : A, fan-shaped colonies of diatoms, 

 Licmophora, attached by gelatinous stalks to seaweed. The repeated divi- 

 sion of a solitary diatom gradually builds up the fan-like colonies. B, 

 Tabellaria, forming colonies grouped in zig-zag blocks. C, Melosira, 

 cylindrical pill-box-like diatoms, arranged in chains. Below end view of 

 the diatom. D, a species of Navicula arranged in gelatinous branches. 

 At right enlarged view of a branch in which the diatoms glide back and 

 forth. After Wm. Smith. 



shaped, curved or straight. They are equally variable as regards 

 their association. Some are solitary and free swimming, others 

 are attached by stalks ; some form bands or ribbons or zigzag 



