508 



A TEXTBOOK OF BOTANY 



[On. XII 



EXPLANATION 



Gametophytes on left, 

 sporophytes on right, all in 

 median section. Shading 

 shows place of photosyn- 

 thesis. Circles are repro- 

 ductive cells: heavy, sexual ; 

 and light, asexual. Signs I 

 and || mean single and double 

 number of chromosomes 



Lines with arrows 

 mean fusion of sex 

 cells, and dotted 

 mean closing of life 

 cycle. Dotted struc- 

 tures are the other 

 generation. 



solid 



FIG. 361. A diagram to show 

 the evolution of the Alternation 

 of Generations. 



The stages, from below upward, 

 are most nearly represented by 

 Protosiphon, Ulothrix, Coleo- 

 chsete, Polysiphonia, Anthoceros, 

 Fern, Selaginella, Angiosperm. 



If from the fourth stage the 

 shaded part of the sporophyte be 

 omitted, and the spores be formed 

 on the unshaded part, the diagram 

 will represent other Red Algse and 

 higher Fungi. 



