The Histology of the Stem of Pontedetia cor data, L. 



THE HISTOLOGY OF THE STEM OF PONTEDERIA 

 CORDATA, L. 



Bv E. M. Wilcox, Columbus, O. 



The histology of aquatic monocotyls has received the atten- 

 tion of few workers. Perhaps the most important contribu- 

 tion to this subject is by J. Duval-Jouve : " Diaphragmes 

 vasculiferes des Monocotyledones Aquatiques," in Memoires 

 de I'Academie de Montpellier, 1873, T. viii, pp. 157-176. 

 Taf. vii. This article is reviewed in Botanischer Jahresbericht, 

 erster Jalirg., 1873, pp. 195-7. Reference was also made to 

 Meyen's Phytotomie, containing a discussion of this subject, 

 to which, however, I have not had access. 



Pontederia cordata, L., is an aquatic plant with thick root- 

 stocks, producing erect, long petioled sagitate heart-shaped 

 leaves, and a one-leafed stem bearing a dense spike of 

 ephemeral blue flowers. The plant is widely distributed, 

 extending from Canada to Florida, and west to Texas and 

 Mexico, not usually abundant in any one place. It is often 

 seen forming a beautiful blue and green covering for a slow 

 flowing stream. 



I have recently had opportunity, in the Botanical Labora- 

 tory of the Ohio State University, to devote some time to an 

 examination of the stem of this plant. The most interesting 

 points in its histology are briefly given below. 



The diaphragms or transverse walls (Fig. i), dividing the 

 continuous air cavities into many chambers, consist of polyg- 

 onal cells with a triangular (seldom rectangular) intercellular 

 cavity (Fig. i, B.) at each angle. These cells contain from 

 ten to twenty chlorophyll grains. These diaphragins entirely * 

 cover one of the air spaces in the stem, but do not, as a gen- 



