168 Causes and Course of Organic Evolution 



and an inner green multicellular mass. The former would 

 be exposed mainly to, and would most strikingly respond to, 

 environal stimuli, by forming hair growths, or protective 

 pellicles or glands. The inner zone, largely devoted to nutritive 

 and respiratory metabolism, would septate off a series of cells 

 that would act as the chlorophylloid cells, would septate others 

 as food storing centers, and would, with increasing growth 

 in length and longitudinal sap flow, evolve long narrow sap- 

 conducting cells. Such conducting cells or zones, at first 

 primitive and soft when the organism was small, would become 

 increasingly large, varied, resistant, and complex in function 

 as the plant attained considerable size. So, for support of 

 the mass, thick walled cells of pure cellulose in many lamellae 

 would first appear, as is still true of many algae and fungi. 

 But, with increasing exposure to aerial strains and stresses, 

 lignified cells would in time more efficiently replace or strengthen 

 the related substance cellulose. Instead of continued and 

 diffuse division and redivision into separate individuals as in 

 Chlamydomonas, continued division would become restricted 

 to definite spaces or intercalated regions amid older tissue, 

 or be restricted to rings. So the original oval or spherical 

 cell would become, as even still is seen in some Acaryophyta, 

 a thread form, next a branching growth, and later a complex 

 plant body. 



Furthermore the same environal responses to stimuli as are 

 seen in Chlamydomonas, continuing to act, would become 

 centered in definite regional cells, but would collectively func- 

 tion in the organism as a whole, similarly to those in the single 

 cell. So geotropism and apogeotropism, heliotropism and 

 apoheliotropism, paraheliotropism, hydrotropism, rheotropism, 

 chemotropism, .and mechanotropism would all be distributed 

 in cells, that would most perfectly contribute to survival of 

 the organism. 



Though some may vigorously object to such a conclusion, 

 for reasons that need not now be given, we emphatically affirm 

 that the above is not a fanciful imagining, but an exact picture 

 of what has occurred in plant evolution. For every step in 



