436 BOTANICAL GAZETTE [june 



j 



longitudinal filaments or medullary hyphae separate, forming a 

 cavity which extends nearly to the tip of the plant. The thallus 

 of the plant is thus tubular in structure. The wall consists of 3 

 tissue layers. The inner layer is composed of 3 or 4 vertical rows 

 of medullary hyphae. Each cell of a medullary hypha produces 

 a radial branch. These radial rows of cells by repeated dichotomous 

 branching, in planes parallel and perpendicular to the surface of 

 the thallus, form the subcortex and the cortex (fig. 10). A branch 

 arising from a cell of a medullary hypha terminates in 64-128 

 cortical cells. The cells in the inner subcortex are not closely 

 packed together. The number of cells in a given area increases 

 as a result of the repeated branching, and thus a compact cortex is 

 formed. The 4 figures for each cell type in the following table 

 indicate the two diameters of the cell as seen in a longitudinal 

 section of the thallus, also the diameters of the nucleus and 

 nucleolus. 



Medullary hyphae 5 2 ■ 2 /* 8.7/x, 2.7/x 1 .0 /1 



Larger subcortical cells 315" 21.5" 2.7" 1 .0 " 



Smaller subcortical cells . . . . 1 1 . 2 u 9 . 1 u 1.8" 0.8" 



Cortical cells 8.4 " 7.0 u 2.8 u 1.4" 



In addition to the radial branches forming the subcortex and 

 cortex, the medullary hyphae may give rise to other branches which 

 remain axial and thus form longitudinal filaments. The medullary 

 hyphae at the tips of the branches and the main axis terminate in a 

 number of short branches composed of small cells (fig. n). No 

 single initial cell could be recognized at the apex of any branch 

 in Dumontia. Branches varying in length from 2 mm. to 4 cm. 

 were examined. The structure of the apex of a branch of Dumontia 

 appears to be similar to that of Furcellaria (Wille 18). Fur eel- 

 laria is cited by both Wille and Oltmanns as a good illustration of 

 the " Spring-brunnen " type of vegetative structure (Oltmanns 9). 

 The holdfast of Dumontia also resembles that of Furcellaria. 

 Each of the medullary hyphae in Dumontia, as well as each of the 

 lateral branches arising from these hyphae, has its own initial cell. 

 Practically all the vegetative cells of Dumontia are uninucleate. 



chromatin 



All 



» 



the vegetative cells in the thallus, with the possible exception of a 



