1909] DORETY—MICROCYCAS CALOCOMA 145 



retained this primitive feature when all the closely related genera 

 have discarded it. 



However that may be, this curious combination of characters, and 

 the absolutely unique archegonial development, are features to be 

 reckoned with by those who, in the future, when all the evidence is in, 

 will be in a position to decide upon the phvlogenetic place of Micro- 



cvcas. 



What 



somethin 



of girdling itself. The theories now in the field approach only 

 remotely to the causes lying at the foundation of the phenomenon. 

 It is probable that it may be relegated , li ke so many other problems, 

 to the domain of cytology. That cell division takes place much more 

 frequently in the horizontal than in the vertical direction in e< 

 Portion of the axis is clearly evident. 



ery 



SUMMARY 



Microcycas calocoma. 



elopment 



germination 



Ceratozamia 



4- here are two cotyledons as in all cycads (except, perhaps, 

 tocephalartos) . 



5 



form one org 



Plumule escaping by bursting the sheath. 



• Mucilage ducts alternate with the 8-10 cotyledonary strands. 

 /• he cotyledonary node is similar to that of Dioon edule and 



stele. 



ozamia 



there ^ h yP ocot yl contains no cortical vascular tissue, although 



9. T e he remnants of a broken-up cambial zone. 

 ba se and 6 VaSCU ! ar strands °f cotyledons and leaves are endarch at 

 throne 6Xarch in the u PP er portions. The exarch condition obtains 



TZ? st of the length of the p etioie - 



is ProcarmY ^ ° f ^ marginal leaf traces takes P lace while the tissue 



may 



