ORGANIC EVOLUTION 



FIG. 99. Diagram, illustrating alternation of generations in the 

 higher green plants. The horizontal lines of figures represent 

 (/, 2, j), successive generations; gametophyte is white and sporo- 

 phy te is solid black ; the egg is represented by circle with central 

 dot, the spores are represented by black dots, of two sizes when 

 differentiated. The types represented are: a, a simple liverwort, 

 (Riccia) ; 6,a more specialized liverwort, (Conocephalus) : c, a moss; 

 a, a fern; e, a horsetail; /, Selaginella and, g, a seed plant (seed 

 in ( ) -marks, above). 



