ANGIOSPEEMS 



343 



represented in the figure the pollen grains would be replaced 

 by mother cells, which form the pollen, or microspores, by tetrad 

 division, as in ferns, cycads, and spruces. The mother cell first 



FIG. 202. Anther and pollen formation in a lily 



A, mature anther with four microsporangia containing pollen grains ; B, the process 



of forming microspores by tetrad division ; (7, gametophyte (g) and tube nucleus (t) 



in a germinated microspore. From Bergen and Davis 's " Principles of Botany " 



divides into two cells (5), with a reduction in the number of 

 chromosomes (consult Fig. 43, 5). These two cells then divide 

 again and form the four cells of the tetrad. Each cell of the 



