FIG. 58. Development of male gametophyte in Asdepias. A-B, A. Comuti; C-E, A. 

 tuberosa. A, section of young microsporangiurn showing archesporial cells; Ji, 

 portion of the single layer of elongated mother-cells; C\ later stage 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 nucleus (<?). A, 

 x 200 ; B-E, x 800. After FRYE.<* 



127 



