152 



GYMNOSPERMS 



HYBRIDS 



Hybrids between Ceratozamia lougifolia and C. mexicana were 

 claimed as early as 1882 ; and there was also a claim that hybrids had 

 been secured between Ceratozamia robtisia and C. brcvifrons. In both 

 cases, seeds were secured which germinated. But, as Helmsley^^' 

 remarked, "There is only one thing certain in all this, and that is the 

 uncertainty of the so-called species." Doubtless, Helmsley was 



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.-/ 



/ 



u 





P- -^^^. 



c 



f 



Fig. 169. — Microcycas calocoma: transverse section of stem just above the cotyle- 

 donary plate, showing the siphonostele condition: A, B, C, D, the four cotyledonary 

 strands ;/',/%/^/^ the leaf traces still in procambial condition. — After Sister Helen 

 Angela Dorety.'''« 



right, for all of these so-called species could probably be raised from 

 seeds of a single cone of Ceratozamia mexicana. 



In the first-mentioned cross, pollen from a male cone of Cerato- 

 zamia longijolia was preserved for 3 years and then used to pollinate 

 C. mexicana. It is possible that the mere irritation of dead pollen in 

 the pollen chamber might stimulate development; but it is certain 

 that the 3-year-old pollen was dead. 



However, the cycads hybridize freely. Of more than a dozen suc- 

 cessful pollinations made at the University of Chicago, two will be 

 described here. 



Zamia latifoliolata X Zamia pumila."^ — On December 20, 192 1, I 

 pollinated female cones of two plants of Zamia latifoliolata with pol- 



