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, 

 Tabcllaria, forming colonies grouped in zig-zag blocks. C, Mclosira, 

 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 



