404 Rennert : The Phyllodes of Oxypolis filiformis 



surface, or sunken slightly below, being about 48 to 54 fx in length. 

 Directly underneath the epidermis is a hypoderm composed of 

 small sclerotic cells with a small lumen. The hypoderm is one to 

 three layers in thickness, and is interrupted only underneath the 

 stomata. The chlorophyl-bearing tissue consists of three to six 

 layers of cells, the outer ones of which are palisaded. The inner- 

 most layers are more loosely arranged. Internal to the chloro- 

 phyl-bearing cells is a cylinder of four or five layers of large thin- 

 walled cells, designated as endoderm by Briquet. The fibro-vascular 

 bundles are situated in this tissue. The pericycle comes into con- 

 tact with the chlorophyl-bearing tissue in places, however. The 

 axial portions of the phyllodes were found to consist of thin-walled 

 stellate elements which are in contact at the tips of the rays. The 

 septa were found to be composed of sclerotic cells with numerous 

 branching canals extending radially through the walls. The fibro- 

 vascular bundles are unbranched in the intervals but break up at 

 the septa and form a mesh of anastomosing branches, which how- 

 ever do not traverse the septa radially to any great distance. 



Briquet explains the seemingly anomalous possession of trans- 

 piration-hindering hypoderm by this marsh plant by the fact that 

 it is subject to two extremes of conditions. The mechanical ad- 

 vantages from the cylindrical form of the phyllodes, and the aerat- 

 ing capacity of the stellate tissue would be of advantage during 

 the early spring season, when the plant is more or less submerged. 

 The shape of the leaf would present a reduced surface and the 

 hypoderm would check transpiration during the mid-summer 

 season after the waters have subsided. 



My own examination of this plant and the results of the 

 experimental tests made with it have revealed some structural fea- 

 tures not mentioned by Briquet, and lead to a somewhat different 

 interpretation of its adaptative features. 



Some plants brought from Georgia and Florida in 1901 and 

 1902 were grown in the greenhouse under various conditions as 

 described below. The septa in the phyllodes of these specimens 

 were found to consist chiefly of small thin -walled cells containing 

 chlorophyl, and resembling the elements of the other chlorophyl- 

 bearing tissue, with only an occasional thick-walled sclerotic cell. 

 The endoderm was found to be continued on the surfaces of the 



