372 



MORPHOLOGY OF GYMNOSPERMS 



between the epidermis and the tapetum. There are three or four 

 successive divisions from the primary sporogenous cell to the mother 

 cells, the tapetal cells enlarging about them and the wall cells becoming 



Fig. 414. — Ephedra antisyphilitica: i, staminate branches; 2, ovulate branches; 

 5, sterile branches; 4, staminate strobilus; 5, ovulate strobilus; 6, longitudinal section 

 of seed; 7, bracts of the ovulate strobilus. — After Watson (2a). 



flattened. There is not always the same stage of division in a sporan- 

 gium, in some cases every stage from synapsis to completed tetrads 

 being seen in passing from the upper part of a sporangium to the lower. 

 In this division the 12 chromosomes are very evident. 



