VOLUME LIV 



NUMBER i 



THE 



Botanical Gazette 



JULY 19 1 2 



THE DEVELOPMENT OF THE VASCULAR STRUCTURE 



OF DIANTHERA AMERICANA 



W. Ralph Jones 



(with PLATES i-iv) 



In 1907, Theo. Holm (5), in describing the anatomical structure 

 of Dianthera americana^ called attention to the "polystelic" con- 

 dition of the stem. This paper seems to be the only one ever 

 published on this intensely interesting plant. So at the suggestion 



of Professor Duncan S. Johnson, I have made a study of the 

 ontogenetic development of the stelar structure in order to find out 

 how the "polystelic" condition of the mature plant is derived. 



The material studied consisted of seedlings grown in the labora- 

 tory and greenhouse from seeds collected near the Chain Bridge 

 (over the Potomac River about four and one-half miles above 

 Washington, D.C.), of seedlings collected at the Chain Bridge, and 

 of mature plants from Chain Bridge and from near Betterton, Md. 



Most of the material studied was imbedded in paraffin, and 

 sectioned 5-10 p thick. Various stains were used, but the best 

 results were obtained with methyl green and acid fuchsin. 



Dianthera americana is a perennial herb, with an erect stem 

 3-9 dm. high, grooved and angled, usually simple, and having 

 opposite, simple, linear-lanceolate leaves 75-150 mm. long and 

 6-15 mm. wide. At the Chain Bridge, the plant grows in the tide 

 pools on the rocky flats on the north side of the river, and also along 

 the banks of the Chesapeake and Ohio Canal, which at this point 

 runs parallel to the river just back of the flats. The plant produces 

 flowers from May on through the summer, ripening its fruits from 



