PHYSIOLOGY OF REPRODUCTION IN PLANTS. 257 



duction in plants. What is meant by " Die ungeschlecht- 

 liche Bildung von Keimen unterbleibt bei den Bluthenp- 

 flanzen " (p. 162), I do not quite see, unless the author denies 

 that pollen grains are spores, etc. Mobius regards sexual 

 reproduction as advantageous in three ways, (i) Legitimate 

 crossing of individuals helps to fix the characters of the 

 species, (2) Crosses of more remote individuals offer in- 

 creased opportunities for variations on which natural 

 selection can work, and (3) sexuality gives a means for 

 developing more complex and highly differentiated forms. 



H. Marshall Ward. 



18 



