1907] CHRYSLER— POT AMOGETONACEAE 185 



traces. In Zostera and Cymodocea, however, there is a system of 

 cortical bundles which are connected with all of the principal leaf 

 traces except the median one. 



5. The circle of collateral bundles found in the floral axis in 

 Potamogeton and Triglochin is regarded as a relic of the ancestral 

 dicotyledonous condition of the vascular system. 



6. The evidence afforded by the vascular and floral structures 

 indicates that Potamogeton is the most primitive genus of Potamo- 

 getonaceae. It shows more clearly than the other genera features 

 characteristic of terrestrial life^ though some of its species are appar- 

 ently reduced forms. 



7. Species of Potamogeton having both floating and submersed 

 leaves and a central cylinder in which the bundles run separated from 

 one another are regarded as the most primitive members of the genus. 

 P. pulcher fulfils these requirements. 



8. The other genera of Potamogetonaceae show further stages of 

 reduction in accordance with their totally submersed habit. Their 

 relationships are in some cases show^n by the vascular structures. 



g. In Naiadaceae the reduction is carried to such an extreme of 

 simplicity that the affinities of the family are obscure. 



lb. Aponogetonaceae and Juncaginaceae are more typically mono- 

 cotyledonous in their structure, and do not seem immediately related 

 to Potamogetonaceae. 



Harvard University 



LITERATURE CITED 



Anderson 



der Monocotylen. Review in Bot. Centralbl. 38:586, 61S. 1899 



2. BORNET 



An 



Bot, V. 1:1-51. ph. i-ii. 1864 



3- Campbell, D. H., A morphological study of Naias and Zannichcllia. Proc. 



Cal. Acad. Sci, III. Bot. 1:1-61. pis, 7-5. 1897, 

 4. Chatlnt, G. a., Anatomic comparee des v^gftaux. Paris. 1856. 

 $• Chrysler, M. A.. The develooment of the central cylinder of Araceae and 



Liliaceae. Box. Gazette 



6. 



grasses 



906 



DeBary, A., Comparative anatomy of the phanerogams and ferns. Eng. 

 trans. Oxford. 1884. 



