CHAPTEE VII. 



THE GENEUAL SHAPES OF PLANTS. 



§ 217. Among protophytes those which are by geneittl 

 consent regarded as the simplest, are the Protococci. As 

 shown iu 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 Protococciis nivalis, which colours red the snow through 

 which it spreads with such marvellous rapidity, is subject to 

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

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

 individual 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 

 symmetry 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 DesmidiacecB and 



