CHAPTER VII. 



THE GENERAL SHAPES OF PLANTS. 



§ 217. Among protophytes those whicli are by gene;.al 

 consent regarded as the simplest, are the Protococci. As 

 shown in Fig. 1, they are globular cells presenting no ob- 

 vious differentiation save that between inner and outer parts. 

 Their uniformity of figure coexists with a mode of life involv- 

 ing the uniform exposure of all their sides to incident forces. 

 The Protococcus nivalis, which colours red the snow through 

 which it spreads with such marvellous raj)idity, is subject to 

 no constant contrasts in the amounts of light, heat, air, or 

 moisture, on its upper and lower surfaces. For though each 

 indi^ddual may have its external parts differently related to 

 environing agencies, yet the new individuals produced by 

 spontaneous fission have no means of maintaining parallel 

 relations of position among their parts. On the contrary, 

 the indefiniteness of the attitudes into which successive 

 generations fall, must prevent the rise of any unlikeness be- 

 tween one portion of the surface and another. Spherical 

 sjTnmetry continues because, on the average of cases, inci- 

 dent forces are equal in all directions. 



Other orders of Protophyta have much more special 

 forms, along with much more special attitudes : their ho- 

 mologous parts maintaining, from generation to generation, 

 unlike relations to incident forces. The Desmidiacece and 



