GINKGOALES 



193 



Cycadofilicales. The known stamens of Cordaitales are differenl 

 (p. 172), but it cannot be supposed that the stamens of so great a group 

 were uniform in type. 

 In fact, in Antholithus 

 Zeilleri, which is re- 

 garded as the stami- 

 nate strobilus of Bat- 

 era (a mesozoic mem- 

 ber of Ginkgoales) , the 

 sporangium-bearing 

 structures are dichoto- 

 mously divided, dorsi- 

 ventral organs, the 

 ultimate divisions of 

 which bore eight 

 sporangia (49). This 

 structure seems to be 

 widely different from 

 the stamen of Ginkgo, 

 so much so as to raise 

 the question whether 

 this Antholithus be- 

 longs to Baiera, and 

 hence to the Gink- 

 goales; but if the 

 sporangia are ter- 

 minal, the parallel is 

 found in the known 

 stamens of ' Cordai- 

 tales. If the sporangia 

 are abaxial on the 

 ultimate branches, 

 rather than terminal, 

 the reduction to a 

 single branch would 

 represent the stamen 

 of Ginkgo. In either 



Figs. 21(5-221. — Ginkgo biloba: fig. 219, voung 

 staminate strobilus in September, showing niicrosporo- 

 phylls with sporogenous tissue and mucilage ducts; 

 X20; fig. 220, young sporangium; the four cells in 

 which nuclei are shown have come doubtless from a 

 single archesporial cell; the two inner cells are 'spo- 

 rogenous and the two outer tapetal; X485; fig. 221, 

 a rather late stage in the formation of a mucilage duct 

 in the hump; the sporogcnous-like cells are breaking 

 down and the surrounding cells resemble a tapetum; 

 X485.— After Miss Starr (53). 



