Fig. 58. —Development of male gametophyte in Asclepias. A-J>, A. Cornuti; C-E, A. 

 tuberosa. A, section of young mierosporangium showing archesporial cells: £, 

 portion of the single layer of elongated mother-cells; C, later 6tage showing two 

 mother-cells, the lower one dividing and showing 10 chromosomes, the gametophyte 

 number; Z>, second division of mother-cell, by which the row of four microspores is 

 formed: E, microspore showing tube nucleus (t) and generative nucleu6 (g). A, 

 x 200 ; J3-E, x 800.— After Fbye." 



127 



